Hi,
You config can be enough for win and old game on a old mame or a fastmame.
The coolest front end requires often more power too. AtomicFE will run on your config but avoid animated layouts. Mamewah will run too i think. But i won't bet on FE like GameEX that is really heavy due to the .NET layer.
But i think you will be more confortable in term of performance under MS DOS. But before starting to choose DOS. Keep that in mind :
-If you don't have a real soundblaster card or you are not sure to find DOS driver for your sound card, you should go on Windows , because mame without sound.... not very fun...
-If you plan to use USB Device (like joystick) , avoid dos too if you don't now where to find driver for your mother board. and if it exists.
-if you want connect to a real 15khz Arcade screen using VGA , dos solution is cheaper than windows one. Under dos a drivers called ARCMON.SYS exists, under windows you need to buy an ArcadeVGA or use PowerStrip (but hard to configure and not compatible with all video card).
-And the last point, is how are you confortable with dos.
So, now, you can make your choice. Both solution have advantages and disadvantages..