Intel CPUs + limited budget can = cutting corners. If you really want to build an Intel based system (a fairly fast one, though not nearly as fast as you could get if you went AMD), this is what I would do: Get yourself a P4 1.8A (that A is IMPORTANT). If you can only do one thing right on this system, do this. This is the new Northwood core P4, not the old underperforming "Willamette" core. You are going to need a socket 478 board. For cost reasons I'd find a board that uses PC2100 DDR ram. (DDR266) Asus is the brand I recommend. If money is really tight, the SiS 645 chipset based boards are pretty good and much cheaper than the i845D chipset boards. (Slightly better performing as well if you spend the big bucks to get PC2700 (DDR 333) ram.) I recommend you use Crucial (
http://www.crucial.com) ram. If you can afford it a GF 3 Titanium 200 or Radeon 8500 plus a good 7200 rpm hard drive as well. I used to recommend IBM harddrives, but it seems they may now be having some issues. The fastest current hard drives (IDE) are made by Western Digital and a very few select ATA133 Maxtor drives. I've had a couple WDs fail on me recently though, so I don't know that they are any more reliable than the very fast and quiet 60GXP and 120GXP series IBM drives.
Contact Skuzzy if you want some more information on building and configuring such a system optimally.
I won't try to persuade you to go with an Athlon XP, but I would advise you to look at
http://www.anandtech.com so you can get some idea on how the chips stack up vs one another. They also often publish pricing guides, which is what you should really be looking at.
Either way you go, realize that it is likely anything you build at this point will have limited CPU upgradability options. Intel is changing their FSB speed (which may make some current boards unable to accept >2.4 Ghz P4s). AMD is releasing an improved Athlon XP this month and a whole new processor design at the end of this year. I do not know if the new Athlon design coming later this month will be compatible with current socket "A" (socket 462) boards. I do know for a fact that AMDs "hammer" (probably going to end up being called Athlon 2 or something else uninspiring) will certainly require new motherboards.
Depending on how long you wait to do this, look and see if USB 2.0 is available on the board you get. Some boards are starting to include it now. Serial ATA is probably too far away to be available within the timeframe you will be building your system. Also be aware that P4s require a special powersupply connector, meaning your current case and powersupply are not likely reusable.
You can reuse your floppy, sound card, CD drives, etc and save yourself some money.