Hmm, the reason straight away to why it'll be loading up slowly is the specs. That K7 505mhz procesor won't be doing it any good.
The reason it might have gotten slower than previously might be because that XP installation has been on for a long time, and so files have moved all over the place, and the computer will take longer to find all the nessacary files.
In this case, go into Programs, Accessories, System Tools, and then Disk Cleanup. After that has loaded, select everything to be cleaned, and let it do its job. That will get rid of alot of rubbish.
Now, go into Safe mode (f8 at bootup) and go to Programs, Accessories, System Tools, Disk Defragmentator.
That might take about 4 hours, but it will sort your hard drive out, putting all the files it needs nearer to the middle of the disk so it can load them faster, and also place them closer together. This may speed it up alot, especially if you haven't ran it before.
FORMAT DRIVE AND START OVER:
If that doesn't work, the only option I can think of would be to format your drive, and re-install Windows on it, and this would definietly give a speed boost. It may also fix that annoying problem with it not switching off, as this could be a driver conflict.
So this is the best option if you are able to spend a little time backing up before hand.
I hope this helps