I would say it all comes down to what you are doing with your program. I did some GDI stuff and on my laptop it worked fine, its a P4 1.8 with 256 ram running XP Pro, but when I used it on another laptop with a P2 233 and 64 ram running XP Pro it was very slow and painful.
If your forms have heaps of controls or graphics then a decent computer would be needed.
Best way to try it is to be able to run your software on a variety of machines and test it all out