mmmm Win98 is out the door. W98 SE is good and stable. WinME is more stable, supposedly, and a halfway house to WinNT. DONT upgrade from win95/98 to winME- it runs like a dog, though a fresh install is fine. Absolutely NO DOS support on ME, but that's only of real use for diagnostics/old school boys.
The best,if you are not planning any fancy hardware in Win 2000 (W2K). Absolutely 100% rock solid, excellent memory and resource management and essential for serious trading platforms/traading.No DOS support here either.
I run W2K for my serious trading, and W98SE at home.
Click "Start" select "Run" and type "msconfig" hit return.
You will see something like the attached screenshot. You can unselect the programs you do not want to run at startup and that should help. Then hit OK and when you next boot up you will get a message warning you that you have altered the msconfig file but just ignore it.