AMD k6-2 my moms friend gave me a compaq presario 5451 with amd k6-2 processor 550MHZ, its OS was 98 and then i upgraded it to xp1 then i noticed that its clock speed decreased to 250MHZ, what can i do to speed it up again?

Windows 2000 is NT based like XP minus the eye candy and has lower CPU and memory requirement.

ME is nothing more than re-dressed 98 anyway and still is running on top of DOS. Forget about ME. I could never understand why people bring it up.

2000 is NT version 5.0
XP is NT version 5.1 = only a small kernel revision higher than XP anyways.

I know that 2000 runs very well on K62 systems that are too slow for XP.

The problem is xp which makes with an older K6-2 the clock speed lower. It takes a lot for a machine to run XP.
The best way is either go back to 98 or the only way could be ME.
not much what you can do about it otherwise