I just installed Avast free after using AVG free for a long time. I like Avast a great deal,
but I have noticed that when I download a page with graphics that the download halts
part way through the page before it finally completes. It really is much slower that AVG
and while I suspected the browsers (Chrome, Firefox and IE8), when I disable Avast
for 10 minutes, the problem goes away. Do you guys have any suggestions? I amusing
Windows XP SP3+, have a 16.GHz processor with 2GB of memory. 
Did you change any avast! settings?
Did you keep AVG toolbar?
Which is your firewall? Any other program that could be interfering?
Welcome to avast! forums! 
I had a similar problem. My experience might possibly help you.
I firstly used CCleaner to clean out old temp files and old prefetch entries, also old directories under program files, program data and user data from any previous security software, then rebooted.
Then i used the CC registry cleaner and rebooted again.
I then installed V7 of Avast rather than v8. to avoid automatic upgrade need to do this with internet diconnected. When installed, I selected the option for the program not to update itself automatically (I do not want V8 due to problems and GUI). Also I unticked Webrep and Sitecorrect under browser protection (I know what I am doing, but others may need / want these enabled).
Then rebooted and reconnected internet cable to PC. All running smoothly with no lag / delay in browsing. Hope this helps.
Thanks for the idea. I followed your advice and my system would not start after reboot.
I had to start up in Safe Mode and remove V7. I am now back a version 8 and hope the
team will figure out why it slows down with any browser.
I have discovered that the element that slows the browsers down seems to be the Behavior Shield
settings. I have disabled Rootkit and unauthorized modifications and it seems to have significantly
improved performance. What I don’t know is how to remove the ! symbol from the system tray…any
help is appreciated.
16 GHZ Processor ? ???
Seems legit
I noticed the same problem today when I installed free antivirus v8.Before I had Bitdefender and it was moving much better.I read the posts above but I don’t want to disable any features because they are making avast unsecure.Any sugestions?
I dont think the behaviour shield would interfere with the network.I would suspect the web or network shield more.
These shields by their very nature can slow browsing just slightly.
If i may make a suggestion.Have you removed the phantom devices from device manager notably in the plug and play section.
I was experiencing something similar on another program and i discovered phantom drivers were causing an issue.
Also i would suggest downloading and running the avast uninstall utility and then attempt another clean install.
But as is said before when i was having network issues it was old legacy network drivers from old programs which were the cause.
Thanks.
Don’t install the addblocker that comes with avast, and turn down the sensitivity on websheild, this will speed up things, the addblocker is really bad, slow as hell. As for webrep, just don’t install it, its pointless, avast still protects you from dangerous sites.