Dimension L Power Supply

If you contact Dell spare parts they would be able to get the appropriate power supply for the motherboard that you want to install.

I don't want to rain on your parade but this project isn't the most cost effective way to get a computer that will be truly useful over the long run. You'll be limited by the processor speed and availability, memory capacity and availability, buss speed, and on and on. Another question you have to consider is that will the motherboard and power supply even fit in that old P200 case without a lot of modification? Sure, you can probably get a new (or more likely referbished) power supply from Dell but not at your perfered budget limit of $30. And you can't just use any power supply, irregardless of the desired wattage, because of the proprietary power connections required by the Dell motherboard. With that being said, PC Power and Cooling, Inc. can supply you with a 275 watt unit for that motherboard for $89 http://www.pcpowercooling.com/prices/index.htm or they will custom build a unit if you desire a higher wattage...for a price! Save youself the time, effort, and money and check out Dells sale prices on a recent new or refurbished model. You'll be happier in the long run and you'll be covered by a warranty with tech assistance if something goes wrong.

Good point; I know it wouldn't be cost effective but maybe I shouldn't do it now, just because of all the parts I need and what the grand total would be.  Only wanted to do it for the fun of it (don't need another computer), but I guess I'll just toss the case out instead.  I'd put the case in about 7 out of 10 condition anyway, so yeah.

BP

Don't give up on the idea of building a computer...it's alot of fun and the knowledge you gain can prove invaluable when problems arise (and you know they will ). Check out the articles at Tom's Hardware http://www6.tomshardware.com/ for hardware reviews and AnandTech http://www.anandtech.com/index.html for examples of computer configurations that you can build  . You may want to consider a "bare bones" bundle for your first effort since it takes out some of the guess-work when it comes to matching a motherboard, processor, and memory  in a tested configuration. Some nice kits are available here: http://www.motherboards.com/ and here: http://www.jncs.com/index-mbh.asp (my favorite). Or if you just want to learn about the latest motherboards, go here: http://www.motherboards.org/ . Go ahead, give it a shot...I'm sure you won't be disappointed with the result .

They are fun, I do agree.  I built one for my brother on December 27 (2 GHz Celeron) and one for me on January 8 (3.2 GHz Pentium 4).  I learned a lot with both, and haven't been disappointed with either one!  Both perform flawlessly.  The one I did is the best one I ever used; previously had a Dimension 4100 1 GHz P3 (now my backup).  I'd do another one right now if I knew of someone that wanted or needed one, but maybe later I'll be able to.

Thanks for those links.  I'll check them out anyway.  Motherboards.org is one of the resources I used as I was building both computers.  Great info there.