Generally the max you should put in a given Memory slot is the max stated by MB manuf.
However say the max was listed as 1 gig per slot, it is possible that a bios update increased that to 2 gigs per slot. Normally the Bios will not recognize memory higher than that supported.
Down load Prime 95, install and run for a Min of 4 hours to see if stable, better stability check would be 8 hrs - If no memory errors you should be fine. Monitor your cpu temps for 15 min to ensure not over heating (not a memory problem, would be a CPU cooling problem) then check temps at 30 min intervals for first couple of hours, or until they stablize.
XP, Vista, Win 7 32 bit all will see upto 4 gigs, when 4 gigs are installed only about 3 -> 3.5 Gigs will be available for Operating system/programs. 3 Gigs, as long as not memory issues with prime 95 - no problem.