set a reply-to address in gmail

from this gmail help page:

to define a reply-to address:
1. click 'Settings' at the top of any gmail page, and open the 'Accounts' tab.
2. click 'edit info' next to your email address.
3. click 'Specify a different "reply-to" address' in the dialogue box.
4. enter the address to which you want the recipient(s) to reply.
5. click 'Save Changes.'

alternatively, one can configure gmail to send and receive emails from other accounts. these pages describe how to do that:

http://mail.google.com/support/bin/answer.py?answer=22370
http://mail.google.com/support/bin/answer.py?answer=34528
http://mail.google.com/support/bin/answer.py?answer=22377