I played BC2 on my e8400 system, and it was ok, maxing at 42fps (cpu-limited). Honestly, I don't think you'll be happy with the performance of BF3 on that system. I have't tried it on my e8400 (I actually might this weekend just for kicks), but it really taxes the CPU (and GPU), and yours are both pretty much the minimum specs. Expect something like 35fps at low/medium settings. Also, I'm not even sure 2GB of RAM will work at all.
The VOIP is not yet incorporated into the game, but that's apparently coming in a patch. Right now you can join a "party" via battlelog and voice chat that way, but you really have to coordinate with your squad members to do so.
I don't think you'd necessarily have to spend $1000 to get a system that will run it well, but yes, you'd have to spend something. The gameplay is quite amazing, really, although it's not vastly different that BC2 IMHO - others may disagree. At minimum, I'd look at getting:
(1) 2500k ($200 Black Friday price):
http://www.newegg.com/Product/Produc...BF2011_listing
(2) z68 MB ($100AR for Black Friday):
http://www.newegg.com/Product/Produc...BF2011_listing
(3) 8GB of ram ($30 for Black Friday):
http://www.newegg.com/Product/Produc...&SID=u00000687
(4) an HD6870 ($140AR):
http://www.newegg.com/Product/Produc...82E16814131378
That's $470. Optionally throw in a 64GB SSD for W7 and the game ($95):
http://www.newegg.com/Product/Produc...F-_-20-147-502
That brings you to about $550. That's a big upgrade from your current rig! I'm assuming you could reuse your Vista license (although you should consider W7 if you go with an SSD), DVD-rom, case, PSU, and hard drive.