I found this online, these people claim they put windows XP on a 20 mhz pentium 1 with 32 mb of ram.
I find many problems with this.
1. The slowest pentium 1 was 60 mhz ( a 20 mhz would be like a 80386)
2. A 20 mhz would only support only about 2-3 mb of ram.
3. The maximum hard drive supported by it would be about 1/100th the size required.
4. A computer this old would not support a CD drive.
5. When you install XP, i believe it checks to see if your computer has at least a 233 mhz pentium 2, and at least 64 mb of ram.