Ahh I didn't realise you have tried it. What problems do you have? And are none of them answered on that page?
Off for my dinner now but I'll be back I'm rarely defeated by these old games! so I bet we can get your Thief working. These 2 of mine are exceptions I think.
Ooooh that could be why then! I'm not sure what would happen if I installed Win 98 onto a seperate partition. Cause I doubt my 8800GTX would work too well in that kind of environment. I would be tempted to build an old PC to do stuff like this but it would be overkill for just 2 games I think.
I just wish MS didn't buy up and then kill off the Tex Murphy series :C