Gotta agree, yet differ from ShinSa.
To render, compress, encode, do you want to let your PC crank through the work while you wait?
Although most video editing programs don't take advantage of SMP capabilities, all your other programs will still function while your rendering and encoding is taking place if you have multiple CPU's. Translation: you can still use your PC while the rendering or encoding/compression takes place if you follow the other suggestions at bottom. (The Intel SMP spec incorporates an I/O APIC -- Asynchronous Programmabel Interrupt Controller - which allows something like 50 IRQ's that function differently from a regular IRQ. A standard PIC (15 IRQ's) only allows a single IRQ to function with one device at a time, even with IRQ 'sharing', which uses 'time slices' of IRQ's from multiple devices using the same IRQ [under ACPI].) Additionally, since each process has at least one thread, having multiple CPU's allows multiple thread handling better, or better multitasking.
ShinSa is sortof right about using SCSI though. Because if you really want to do video editing, then you should dedicate at least two new, fast, individual SCSI drives of the same size for video editing. This is so you can work from one drive to the other without interruption. Since IDE would need three IDE channels or more, this becomes more and more unpractical with IDE. Also your primary boot/system drive and swap file/pagefile/drive caching should be independent of the editing drives. RAID may be unecessary when properly dedicating and configuring multiple SCSI drives, although having two RAID 0 arrays for editing is even better. This will also allow you to use your PC while it's doing time consuming functions. If you use RAID, buy hardware RAID.