bulldog7000's advice is sound, though I would maybe look at the Matrox G1000 which is coming out in the next few weeks. This card is based on the new Parahelia core and should give you much better 3D performance if you are going to do other things with this machine(you didn't specify if this was only a DV-editing machine or is going to be your main rig too, so I'm not sure if you plan to run games on it). It should also have an option for Triple-head, which would allow you to have three monitors if you are so inclined. I would wait a few weeks for reviews to come out and see if this card fits your needs better. Otherwise the older Matrox cards would probably be a good choice if you are only going to be editing with this system.
I agree with B-Dogs statment concerning IDE vs SCSI. Save yourself the money and get some nice WD 120GB 8MB cache drives and ATA RAID them. I would'nt get a board with an onboard RAID controller, IMO, even a mid-range add-in card will give you better performance and less issues. I have been running an Adaptec 1200A, which is one of their more basic RAID cards, and it's noticably faster than my onboard Promise RAID controller was.
RAM is also an issue with video editing. If you are doing anything intensive, I'd get at least 512MB, but 1GB would be better as it should definately be in your budget. With a single Proc P4, definately go with RDRAM and get a board with 4 RIMM slots, as I think it is still hard to find RDRAM modules larger than 256MB(Not sure on this, I have all Athlon Rigs). If you go Dual Athlon MP, then you'll be using DDR. I think that you will want to go with PC2700 DDR, because with two CPUs(someone correct me if this is wrong) you will probably have more demands on the memory subsystem than with a single Athlon(whose FSB would be less than than that of PC2700 DDR, and thus would not gain a huge performance increase).
I won't preach on which platform is better, though I do tend to go with AMD rigs for my own use. I think that SMP is rarely taken advantage of in software, though, like RAID, will contribute to the system feeling "snappier" as you will rarely max out the CPU load on both chips(in fact, in un-optimized software, at best your CPUs will each be 50% utilized as the OS will only try to split the load evenly.) You wil need to be running either win2k or XP if you are going to run an MS OS to take advantage of SMP. The P4 has the potential to be faster, but only if the program has been optimized for its SSE2 instruction set. Many popular programs have, which is why their are all these benchmarks showing the single P4 system beating the dual Athlon system. As you are doing video editing, you will probably be using one suite mainly(Premier as you mentioned), which actually supports well both SMP and the SSE2 instructions of the P4. Performance will be good either way with this program, though you'd have to look around for specifics.