I was hoping to get advice on what computer build I should try for. The current ones I'm deciding on are a $400 budget one, $500 budget one, and a $600 budget one..

I'm looking to be ABLE to play games such as Sims 3, Civilization IV, and Europa Universalis III at maximum quality very smoothly. I also hope to play the upcoming games Starcraft II and Civilization V smoothly as well. I have a 19" monitor.

Which build should I go for for an enjoyable time playing these sort of games, while spending the least amount of money possible? And should I make any modifications to a build if I were to choose it?None of the links worked.

In general, the more you spend, unless you do something stupid, the better the machine will be.

BTW, plan to spend $5 on a static strap.Do you need an operating system included within your budget?
What's the most you want to spend?Working links (they had http// - No colon)

http://www.hardware-revolution.com/400-gaming-pc/
http://www.hardware-revolution.com/500-gaming-pc/
http://www.hardware-revolution.com/600-gaming-pc/Alright, thanks for pointing the error out.

I already have the disc to install the OS, so I won't need to include it in my budget.

The bar limit on how much I want to spend is $600, but it's still negotiable.

And I really don't want to spend more on the computer, since I just want the computer to be able to run the programs I LISTED smoothly.The motherboards in the 4/500 builds are bad, the PSU in the 400 build is also bad.
Personally I'd take the $600 build, change the CPU to the X4 635 as it's usually the same price as the 630 it replaces, take G.Skill Ripjaws over the Adata RAM, pick up any brand other than HIS for the 5770 (XFX has the best warranty), probably drop to a 500GB Western Digital Blue/AAKS, Seagate 7200.12 or Samsung F3 HDD as it will be faster, and I'd take a Liteon burner over the Asus but it's no big deal.
I'd most likely pick a different case but that's personal preference, I like the Antec 300 for the build quality and expansion options.
I'd most likely get a different PSU too, like a Corsair 400W.
Just shows how different people's interpretations are heh, the only thing I like about their $600 build is the board.I plan to buy from Newegg.com, so if you think there is a better place to buy any or all parts, please do tell.

The list I've compiled so far:

CPU/Processor - AMD Athlon II X4 635 Propus
Motherboard - ASUS M4A785TD-V EVO AM3 785G
RAM - G.SKILL Ripjaws Series 4GB
Video Card - XFX Radeon HD 5770
Hard Drive - SAMSUNG Spinpoint F3 Internal Hard Drive
Optical Drive - ASUS SATA 24X DVD Burner
Power Supply - Corsair CMPSU-400CX 400W
Case - NZXT M59 - 001BK Black Steel ATX Mid Tower

Grand Total: $644.16 (It'll take me a Daniel Webster to convince my parents to fund this, but it's possible. Just vaguely.)

Note: The Case I've selected comes with a free LOGISYS 480W Power Supply, so I was wondering whether or not this could replace the Corsair CMPSU-400CX 400W.

Are the part compatible?

Question: To what extent of games will I be able to play with this build?I plan to buy from Newegg.com, so if you think there is a better place to buy any or all parts, please do tell.

The list I've compiled so far:

CPU/Processor - AMD Athlon II X4 635 Propus
Motherboard - ASUS M4A785TD-V EVO AM3 785G
RAM - G.SKILL Ripjaws Series 4GB
Video Card - XFX Radeon HD 5770
Hard Drive - SAMSUNG Spinpoint F3 Internal Hard Drive
Optical Drive - ASUS SATA 24X DVD Burner
Power Supply - Corsair CMPSU-400CX 400W
Case - Antec Three Hundred

Grand Total: $629.16 (I'd prefer if I could lower it with little to no loss in performance.)

Are the part compatible?

Question: To what extent of games will I be able to play with this build?

EDIT: I've decided to replace the NZXT M59 - 001BK Black Steel ATX Mid Tower with the Antec Three Hundred. This means the LOGISYS 480W Power Supply needs not be considered anymore.
That Logisys PSU is a piece of junk, good that it's no longer in the picture.
The NZXT case is also not very good build quality, for the price it's also good you got rid of it.
To drop the price, you could get something like an Athlon X2 240/245/250 CPU, which are all dual core compared to your 635 quad - for gaming it shouldn't make much of a difference, not in the near future anyway. I wouldn't recommend dropping anything else down though to be honest - the 5770 is the best value for money you can find right now, and will play just about every game out there at higher settings. It may be a little overkill for what you need right now but it saves you upgrading sooner. If you really are desperate to save a little, you could grab a 4850 or 4870 if you find a good price, they should still give good performance but I wouldn't personally invest money now in last-gen cards unless I got a great deal.