Yeah, but you could be wasting your time, too...
What you need to do first
is to try to speculate why
it is running slow now. For example, is DMA turned-on on your hard disk drives? Does the system have adequate memory? Are particular things running slowly; can you characterize what it seems to be doing when
it is "running slowly?"
Yes, you can speed up a system somewhat by optimizing the kernel. But most things that "slow down" a computer are not caused by sluggish code-paths through the kernel; they are caused by I/O.
For instance, try these two commands and quote the results here. As root:
/sbin/hdparm -Tt /dev/hda
/sbin/hdparm -I /dev/hda
This will give you basic timings, and basic configuration parameters, on the I/O to your primary disk-drive ("/dev/hda"). There are plenty of articles on system optimization on the web, and you should start reading .. before you compile anything.