They won’t conflict (at least with the default installation). But, for sure, you’ll lose a lot of resources and won’t receive the payment for this security.
I mean, the balance will be using one of them, or even none, only an antivirus resident.
If you can test, let us know the results 
Be careful when using comodo firewall and avast! together. Many people are experiencing problems with these two security products running together. To my understanding comodo has acknowledged the problem and is working on a fix. Personally I just use the SP2 firewall in XP. It gets the job done and works just fine. Some people believe it is necessary to have a two way firewall. However, I rely on a multi-layered approach to security. I don’t rely on any single product as the cure all solution.
As far as tea-timers is concerned in spybot, I’m not very familiar with it. Spyware Blaster uses no system resources at all and has received many recommendations. It works without even running in the background to protect your computer from the many active x based spyware programs. It is my opinion that Windows Defender and Spyware Blaster will provide solid protection.
And a quick update. You may want to add SUPERAntispyware to your arsenal. I can see why several people recommend it. It’s a great program. With this program you can run a weekly scan. Combined with good common sense and good internet practices, I believe this will be sufficient protection for anybody. 
Will my system resources be in good shape with just Comodo and avast!?
Most probably, yes.
avast at normal level of sensibility
The latest Windows defender protects crucial areas well, the rest is taken care of by Avast, the two work out nicely for overall system protection.
well i use avast home edition,spyware terminator(a very good real-time anti-spyware) and windows xp sp2 firewall and i scan my pc weekly with spybot s&d on demand…so everything works like a charm with very low resources…i think this combination is suitable to my requirements coz i’re protected without using lots of programs and slowing down ur system…in my opinion a personal firewall is not necessary…it’s useless to use more and more programs…it’s a bit risky what i’m telling u but that’s what protection i use and i have no problems by now…if something wrong happens…i’ll let u know…
Whilst the windows XP firewall is usually good at keeping your ports stealthed (hidden) it provides no outbound protection and you should consider a third party firewall. Network Shield is a very limited specific intrusion detection for common virus attack ports and not a firewall.
Any malware that manages to get past your defences will have free reign to connect to the internet to either download more of the same, pass your personal data (sensitive or otherwise, user names, passwords, keylogger retrieved data, etc.) or open a backdoor to your computer, so outbound protection is essential.
So if your happy with that risk, good luck.
Hi DavidR,
Going that way is not for the average Internet user, if you are an advanced user and have some advanced programs to check on the integrity of your system all the time, and know what that means, well some do. I know the function of a firewall has been downgraded by some 40%, and there is a lot now that can get unto your machine under the radar right into your machine, that is why you need webshield and port 80 scanning with a form of IDS installed. Then it would be good that firewalls could also incorporate some form of extended protocol scanning with a personal configuration where you could block all you do not want to admit or block from going out even at the lowest levels.
To-day multi-level protection is the best thing we have at the moment,
polonus
I’m surprised nobody has mentioned BOClean. I recently abandoned Ewido AntiSpyware (paid version) following AVG’s takeover. I appreciate BOClean works in a different way to AVG/Ewido, but reportedly, is at least as effective, if not more so.
Sorry I don’t see where this relates to my post, basically stating that in BJ_GeOrgE’s opinion, “in my opinion a personal firewall is not necessary as xp sp2 firewall and network shield keeps u safe…it’s useless to use more and more programs…” doesn’t provide adequate defence. This is over an above any other defence you might hav, it only relates to having a firewall that provides outbound protection.
well…for me…if u have a gd antispyware with real time protection so u can prevent keyloggers and other malwares from being installed in ur machine,then u don’t have to worry about hacker attacks…spyware terminator is a kind of firewall coz it asks for every application behaviour…so if an application wants to connect to the internet,u can allow or block her…i know it’s not the best way but i don’t care…it uses low resources and i have no any sensitive data in my machine…neither passwords nor credit cards number etc…i know its a bit risky but it’s fine for me… 
i know it's not the best way but i don't care.. it uses low resources and i have no any sensitive data in my machine..neither passwords nor credit cards number etc...i know its a bit risky but it's fine for me...
As I said previously your system, your choice, your risk, but when offering it as advice when you freely admit it isn’t ‘the best way’ isn’t good advice.
i see…ure right davidR…sry for advising this…i should change my reply…sry again…
No need to be sorry, it is easy to forget that there are some that view the topics who aren’t as experienced as yourself to be able to get away with this security approach. So we have to take care when offering advice just who might read it.
thnx DavidR…next time i will be more careful…