As for a firewall...that is tough. Comodo isnt compatible yet. Most of the other ones i know of are part of a security suite. Zone Alarm is the ony one i can think of off hand that is just stand alone.
According to Comodo's site, v3.0 is Vista compatible...
System Requirements (version 3.0)
Windows XP – 32 and 64 bit versions
Windows Vista – 32 and 64 bit versions
64 Mb RAM
50 Mb free disk space