It's hard to find much info about your Philips Freevents MT2800, Core 2 Duo E64x setup, but I'll bet that you can replace your 2x 1GB sticks with equivalent speed 2GB sticks (to a total of 4GB) - and memory is pretty cheap these days.
Win7 will run in 2GB but is happier with 4GB (as is XP BTW)
I don't know why you are getting different results from the test sites, but they do sometimes get it wrong with uncommon setups like the Philips.
I would try to get away from XP if you can - it was never that secure anyway and this is likely to get worse. Win7 is much better in many respects.
Mac
