Your processor is plain too slow .
This has nothing to do with your HD .
Replace that 400Mhz with something over 1 Ghz and you will see that the HD was not the cause of those "hiccups" .

Most PII motherboards also take PIII's . (the same socket)
And PIII's go up to 1.3 Ghz .
You can still upgrade that machine for a minimal amount of $$$