Sense you ask here is my 25¢ worth. Folks want 16:9 and for your budget go SD. That leaves the
Cannon XL2 at roughly $3500 B&H or the DVX100b at $2400. But some folks say that the 16:9 from the DVX100 isn't all that good (its a native 4:3 camera). Its certainly inferior to the XL2 video, but the audio is much better so you could get by with using camera sound.
If you go 2 part sound then you would record to a separate device like the
Tascam DR100. If you go that route then you need to worry about the cameras and recorder getting out of sync. That will take between 20 and 30 minutes. But if you go with the DVX100b you don't need 2 part sound and things just got a lot simpler (less expensive).
As for computers I edit on a laptop using CS4 and it works reasonably well. I can even edit AVCHD but the DV produced by the XL2 or DVX100 is I frame only and edits better and cleaner. The computer I use is a Lenovo W700ds with system RAID 1 drives and external SATA drives for video. The docking station has an eSATA port so you could just buy a
docking station and some hdd and be good to go. Just buy commodity drives off the web.
I use a external 10,000 Veloraptor drive for scratch and WD ES2/3 drives in RAID1 for the project. You don't need the RAID project drives as if you are late the attorney you work for will not come after you for 10 hours of $5000 an hour expert witness fees. Also that cuts costs some.
The built in audio is good enough for dialog and for spotting music if you use any. I have a 4 core Duo2 Extreme processor and 8GB of memory because CS4 has live links between the programs so you don't need to save a project exit Premiere to use Photoshop then save again and go back to AE or Premiere they are just there. Also render times are reduced with a 64 bit OS.
You really want a 64bit OS for CS4. Vegas is lighter weight and you could get by with less memory. The W700 also has a built in WACOM tablet which IMHO is essential for editing productively.
BTW what mics are you going to use the camera mics will not work.
BTW you eed to use the eSATA connection not the USB as the USB is too slow for editing.