I very recently built a machine. Some of the parts were hand-me-downs, but you might be able to get away with the same.
One thing… yes you should pay attention to what video card you get. But I think the most important part beyond your interface is the motherboard. Dig around the websites of audio interface manufacturers and you will find all kinds of esoteric issues with various chipsets. (For one example, NForce 4 based systems don’t do so hot because of a bottleneck between the PCI and PCIe sides of the system. That one comes right off of RME’s website.)
Anyway, I went for the best bang-for-buck I could come up with yet have a solid, well performing machine…
CPU: $ 70 AMD Athlon 64 X2 3600+
RAM: $ 55 CORSAIR ValueSelect 1GB 240-Pin DDR2 SDRAM DDR2 667
MB : $100 ASUS M2N-E Socket AM2 NVIDIA nForce 570 Ultra
VID: $ 50 MSI NX6600-TD128E GeForce 6600 128MB PCIe x16
HD : $ 95 Seagate Barracuda ST3320620NS 320GB 3.5" SATA 3.0Gb/s
PS : $115 SeaSonic M12 SS-500HM 500W Power Supply $115
FAN: $ 5 ENERMAX UC-8EB 80mm Case Fan $5
I had the following already, so didn’t have to purchase:
Lite-on DVD drive
Old ATX Case (Antec)
IBM M Series keyboard
Kensington Expert Mouse (big trackball)
Total purchases were about $490. Not too shabby.
Of course that doesn’t include an interface yet… I already own an RME multiface and a Delta 1010LT. You could use what you have now and move up to something else later, or try the Delta as has already been mentioned. I’ve seen refurbished Delta 1010LT’s for $150. So that’s $640. In the ballpark, at least.
– I used the stock Fan/cooler for the CPU… For about $30 you could get a much better, quieter one.
– The Corsair ValueSelect tends to be on the cheap side, but reliable. Never had trouble with any of it yet.
– That motherboard is solid, has good linux drivers all the way around, and is quiet/fanless. (Built-in-heatpipe.)
Be sure to stay away from budget chipsets, and do research on how well supported they in linux AND with any audio interfaces you want to consider. For an AMD system you can’t beat this one. It doesn’t have built-in firewire, but most audio folks recommend TI chipsets for that anyway, which rarely come on-board… forcing you to disable the on-board firewire and purchase a separate card anyway. So no loss there.
– The vid card is maybe overkill for this purpose, but does a decent job on older games if you need a break from work. It also has VGA and DVI-I output , so should be able to handle dual head with either analog or digital monitors. (LCD would be great, but being able to push two old crt’s is better than not being able to.) I purposely stayed away from ATI, for the same reasons someone else mentioned. The standard GeForce 6600 seemed to be a sweet spot for power/price/features/support. The only problem is it has a fan. I tried to find a fanless card in this range (that didn’t use turbocache or other memory sharing garbage) but didn’t come up with anything. Maybe a passive cooling add-on for it might be in order at some point.
– The power supply is a tank with plenty of good solid power. Very quiet, with a modular cable system, too. I decided to put my money here rather than a case with a lesser power supply, as I had a decent old ATX case available already. (With an older power supply that wouldn’t have been up to snuff.) At some point I could move up to a nice rack case, and I’ll already have the PS I need. (Many come without a PS.) A lot of folks in pro-audio forums reccommended Seasonic, and so far I agree.
– The case fan might not be necessary, but that has a frictionless magnetic bearing… Very quiet and not likely to ever become a noise problem. Fairly cheap, too.
If budget allows, I recommend
doubling the memory
adding a second hard drive (separate system/audio data)
a better cpu fan (zalmann or something)
a fanless 6600, or 3rd party passive cooling solution that works well with one
At that point you would have nearly the equivalent of a machine from a pro-audio builder, but for much less. (I actually talked to a few when planning this one.) The biggest difference would be the case, but you’ve saved plenty of scratch to fetch yourself a snazzy rack case if you want, and still have some left over.
Also, whether you go with AMD or Intel, GET A DUAL CORE. You won’t be disappointed, and Ardour is very slick with it. Even if it doesn’t fully utilize both cores, just the separation of the gui and the engine side of things makes a huge difference.
FWIW I put Ubuntu Studio (just released) on this new machine just this weekend without a hitch, and was rockin’ away in no time.
At any rate… Good luck.