snooggums said it perfectly.
We just don't know about BF:BC yet, though we do know the official requirements
Link:
Battlefield Bad Company 2 and 1943 system requirements revealed

Minimum Frostbite PC Specifications for BFBC2 & BF1943

• Processor: Core 2 Duo @ 2.0GHz
• Main memory: 2GB
• Graphics card: GeForce 7800 GT / ATI X1900
• Graphics memory: 256MB
• OS: Windows XP
• Free HDD space: 15GB for Digital Version, 10GB for Disc Version (BFBC2); 10GB for Digital Version, 4GB for Disc Version (BF1943)

Recommended Frostbite PC Specifications for BFBC2 & BF1943

• Processor: Quadcore
• Main memory: 2GB
• Graphics card: GeForce GTX 260
•Graphics memory: 512MB
• OS: Windows Vista or Windows 7
• Free HDD space: 15GB for Digital Version, 10GB for Disc Version (BFBC2); 10GB for Digital Version, 4GB for Disc Version (BF1943)

That being said, it means absolutely nothing. I have seen lots of games that the "recommended" hardware gives you nowhere near the eye candy you want.

And you mention the 5770, which from what I have seen is a decent card, but you say you want something that is going to be good long term, and I don't see that lasting too long. Maybe a year, just like a year from now the 260 will be feeling somewhat long in tooth with the games that will be out and the latest hardware. But you have to get what your budget allows.

If you are really really hurting right now for a new system (your FPS in the games you play now are dismal, even on low settings), then we will put together some options for you.
But if you are doing fine to get buy for a few months till we know more, that's cool too, and I suggest to check out this forum as we do a good job keeping TG up to date.

As for buying things like bundles, most all of us fondle Newegg constantly (I check the Intel SSD prices at least 3 times a day since they keep messing with pricing).
To get the best deal, the way to save money is to narrow down your parts list, like say a new Asus motherboard. Then look through at them so they are sorted by buyer ratings. Look through the top few rated ones in your price range for the one that has all the features you want. Then, go to that page and look at the combo deals (on the left side toward the bottom under the pictures.) Look through and find what other part you need that gives you the best discount. Then do the same with the other parts. I've helped guys put together builds that saved $150 that way.

You can also catch deals at stores like Fry's where they will do CPU/Motherboard combos, like the one I posted about here:

Core i5-750 Processor + Gigabyte GA-P55-UD3R Motherboard $200AR @ Fry's B&M

The best thing to do, and what most of us do, me included, is buy parts over a few months, getting the best deals when you see them. It sucks something horrible to have most of the parts, but you are just waiting on a good deal for that one last piece, and you can't do anything but wait. Because the wife is hiding the credit card But I wouldn't know anything about that

So start planning now, and by end of Feb. or so you will have a really awesome rig that will last you 2-3 years of very good gaming. I promise you a $500 (total) PC is only going to make you happy for a year or so.

You are going to need the following with a VERY basic estimate of price:
PC case ($60-$130)
PSU ($60-$115)
RAM ($50-$150) -prices are a bit crazy right now and are supposed to go up
CPU ($175-$300)
Motherboard ($125-$175) -really depends on features and sales
Video card ($150-$350) - Will really make a huge difference in when you have to upgrade again
Windows7 ($100)

DVD Drives ??-- If your current ones are SATA, could be reused, but would hurt resale/usability of your current computer and they are only $30. ($20 for a DVD-ROM)
Harddrive??-- You said you have a big one, but might be better to just get a new one and keep your old rig running - ($50-$100)

So you are looking at about $800 if you pick and choose everything on the low end, or get get really good sales on stuff. Like the Antec 900 case thread the other day where it was on sale for $60, but normally is like $115. But $700 broken up over 3 months or so isn't that bad.

Also you can keep an eye on or search sites like
http://slickdeals.net/
http://www.techbargains.com/
http://www.logicbuy.com/
You can find amazing deals.

When it comes time to pick the parts, just ask in this thread and we will pic out some good choices. And look at the stickies at the top of this forum. That will also make putting it together super easy.

Just reading back through this, I hope it doesn't come off as me talking down to you. You said you were clueless, so I just started typing, and ended up here. Hope it doesn't put you off or anything.