Hardware Problems

I have upgraded my computer to:
P4 2.8E GHZ
512 MB ram
P4P800 Asus Motherboard
Geforce 2 MX400 (From old computer)
DVD & Cd Burner (From old computer)
Maxtor 40Gb 2Mb cache 7200 RPM 100ATA (From old computer)
IBM 12 Gb 2mb cache 7200 RPM 66ATA (From old computer)
O/S Win ME

My computer is choppy in everything and very slow. My CPU
temperature never goes over 49C / 120F. I have no
hardware conflict and have all up to date Drivers.

I have run the PCpitstop benchmark and some others and
obtained those results:

-My harddrives score very low at 0.36 MB/sec
(I had run scandisk and Defrag before testing session)
-My CPU load is alway at 100%
(I had disable CPU cooling software)

This new computer run slower than my PIII 500 MHz. I had
to disable HT tech because ME doesn't support it.

What can I do to get some speed:
Is my video card slowing everything down?
Should I update to Windows XP?
Any solutions out there....

Thanks

Pat