I'll come swinging to the rescue here, and first of all answer your first question, i have used Excelsor in quite a few budget computers i've built before.
The Excelsor range of hard drives are exclusive to the UK as suggested before, they are actually quite reasonable drives, they are budget hard drives, for budget builds / upgrades in older systems.
I have two of the 60GB IDE 7200rpm 2mb Excelsors running in my Gentoo Linux box, i've had them for over a year and a half of solid use without any problems.
This drive is perfectly ok for any computer, although performance wise it's more suited to a storage / backup computer or an older system such as your pentium 3, or non-gaming machines.
As for your PSU, your PSU is labeled as 230W, this is your MAX output, ie, if pushed as far as it could go due to the power consumption of your computer, it technically should be able to produce 230W of power (but would most likely either not produce that, or blow/fry on reaching 230W).
Before you get worried, i must tell you the first thing u must know about PSU's is the fact that the Wattage (too a certain extent) doesn't mean jack-shit :)
A PSU has several different power outputs to your computer, these are called "Voltage Rails", each Rail outputs a necerssary different Voltage, on every ATX PSU today you will find these rails:
+5.5V / +12V / -12V / -3.3V and a few more i can't be bothered to list
anyway, you're computer requires your PSU to contanstly provide 5.5V (+/- 5%) to the +5.5V line, if it provides to muhc power it will damage your components, and if it provides under 5.5V you will experience problems with the hardware as it is not being powered correctly.
The voltages on your PSU are determined by your PSU's Amper output (Amps) on each Rail. These typically range between 0.3A-40A.
If you look at the label on your PSU you will understand this alot clearer.
Anyway, you're answer.. Yes 230W of your powersupply even if it is a cheap generic low end psu should be enough, although if you have a Phase Change cooling unit cooling your P3 & ur overclocking it by 2GhZ then no.. it wont :) - but i doubt ur doing :) (2Ghz = slight exageration).
I hope this helps. And if you do have any problems with your computer, disconnect the power to some components so you're JUST running the minimum to run ur computer (video card / 1piece of memory / 1 hard drive with OS on) then add the rest gradually until the problem reoccurs. Then you know what the maximum combination of hard drives / memory sticks / cds are for your power of PSU.
Long but i hope.. helpful.