I just went thru looking at options for using my old pc, and I came up with “remote access” and it works like a charm. Its free and works on my new XP system and my old Win 98 system. This program is Tight VNC which is the same as “go to my pc” as far as I can tell. You’ll need a router, which is pretty cheap if you don’t already have that. Probably work for you too?
PS–I recall now reading that KVM switches were very sensitive about the connector? Many of them won’t work with a usb-converter (but some will?). If you are using one, going to a straight pci2 (?) type mouse might work? This was actually one reason I kept looking. Compatibility with long established standards–you’d think things would work, but they don’t.