Will Avast scan email other than outlook, for example, Yahoo, Excite or MSN’s Hotmail?
Only if the incoming mail protocol is POP3 or IMAP4.
As I know, avast! works with these Internet Mail Clients: MS Outlook (including Outlook 2003), MS Exchange, MS Outlook Express, Eudora, Pegasus Mail, Netscape Mail, Mozilla Mail, IncrediMail and The Bat! 
That’s only the case with the Mail Protection Wizard - i.e. the ‘automatic setup’ thing.
If you’re able/willing to do the config manually, avast can protect any SMTP/POP3/IMAP4 based mail client.
Vlk
Outlook(or any other similar mail client) uses POP or IMAP protocol which is scanned by Internet Mail provider(or Outlook provider),for Yahoo and MSN its used a Standard Shield. When you view Hotmail or Yahoo Mail,files in browser cache are scanned by Standard Shield and when you download attachement form such web based email,they’re also scanned by Standard Shield.
If someone can give me the directions to do it i will.
Hopefull, it will work, I like Avast so far.
POP: localhost
User: your_username#pop.something.com
Pass: your_password
SMTP: localhost
User: your_username#smtp.something.com
Pass: your_password
Just type in these informations in any mail client.
I think you can use this for MS Outlook too if you didn’t install Outlook/Exchange provider.