ok.
first of all, i use a celeron 3.46ghz processor (533 bus LOL!) and THAT sucks, so whatever you've got isn't that great either. and no, your mobo won't support anything newer or better.
if you know someone who knows computers, i'd recommend getting them to put this together into a new computer:
-c2d allendale 2 ghz processor - 135$.
-this or this would be good mobos to look at. both under a hundred.
the ecs board takes ddr2 800 ram, and this is a good one to look at, and the asus board takes ddr2 667. in general, look for one with lower CAS latency and a heat spreader, that'll speed up your machine. patriot's memory comes with a lifetime warranty, which helps out a lot. both under 45 dollars.
-you'll need a cpu fan, of course (30 bucks).
-a few hard drives (i'd suggest one or two at 7200 rpm for backups and files and one at 10,000 rpm for those music samples and heavily-accessed files. that'll be a big chunk of your cash, around $250 or so for all them.
-a case is recommended, of course. this one's 40 bucks, it's a cheap and a solidly constructed case.
-if you need a graphics card, the one i've got is absolutely fantastic - while a graphics card isn't needed on a music computer i'm sure that you game some as well, and this can handle even the newest games on my pos homebrew (3.46 celeron, 1gig ram, this card). 80 dollars. also, it's got two outputs that can be used by monitors, so you can run dual-monitors quite easily.
-for a music computer, a good sound card is required. i use this and have never had a problem with it. i prefer external sound cards because it's one less thing in your case. 45 dollars.
-a power supply. this is a pretty good one.. rosewill makes good products for relatively cheap, and they come in good packaging. i've bought six and never had a problem caused by them (dropping it does break it, though, thank god for RMAs).
-obviously you need a cd/dvd drive as well. this one's solid.
did i miss anything? you might want an external hard drive as well, and some good speakers and a nice pair of headphones, but this is the computer end of it.
that adds up after a bit - you're looking at about $800-$825 for a really nicely built computer. that's including shipping costs.
i'd put it together and ship it to you, but norway's a long trip =)