I have tried using Connectix Virtual PC (now bought out by Microsoft and I can't remember what they've renamed it) as well as DosBox. Both are good at what they do and have enabled me to run quite a few old programs. I can't get the one I REALLY want to play to work satisfactorily though ... Syndicate Wars!!
I LOVE this game and used to play it for days on end on my old Pentium 90 back in the day.
On my new PC though (Prescott 3.0Ghz), it will load and run on both VirtualPC and DosBox, but I simply can't slow it down enough to make it playable.