Good OS for old gaming

Hey Community!

So i have my old PC laying around doing nowt atm, its got a Intel Pentium D 915 2.8Ghz 4GB RAM and a Nvidia 250 GTS inside it, and am thinking of games like Theme Park, I-Ninja, Sim City 4, and other low powered games.

What OS should i go for, im thinking W7 Ultimate 32Bit seeing as i have a disk for it.

Any suggestions?

Thanks in advance!

i would partition the drive, put windows 98 on one partition, and xp on the other. and if you want to play any OLD games, throw dosbox on the xp side and use that :)