I understand where your coming from. I just upgraded my son's computer and only had about $200 to do it. I had a e6700 already

, but would've went with AMD, since I can get a decent mobo w/decent options for less $ than an Intel one. A ~$65 AMD mobo w/a ~$70 CPU (x2 4200) is a nice cheap option (~$135 total). Now a Intel e2140 ~$74 and a p35 mobo ~$90 is a nice option, but you'd need to OC the e2140 just a bit to make it better than the x2 4200 (~$165 total). Sometimes when I'm building a system a $30 price difference ($135 AMD vs. $165 Intel) will make or break the budget. Yes the $30 on the current performance KING (Intel) would probably make more sense, but with TF2 and CSS being your primary games, you won't need anything too demanding, especially with a 8800gt under the hood.
With you having a tight budget of $200, I'd much rather go with an Intel build, but your the one making/spending on the build, so AMD build is what your going to get. I think your ideas for a nice Phenom in the future is honorable, since I'm sure AMD should not make this mistake anytime soon (if they want to have a future). I'm also hoping that they get the Phenom done right and give Intel some much needed competetion.
So to sum it up:
NO OC'ing (as you stated), limited budget, and Phenom upgrade later = AMD x2 CPU and AM2+ mobo (as you linked). Only issue is that you'll not be able to take advantage of the Xfire option on the mobo, since you have an nVidia GPU. You'd need any SLI mobo to have 2 nVidia GPU's, but that my not be an issue with you. If I was getting that mobo you linked for the AMD AM2+, I'd be getting the 3870 or 3850 and then buying another when/if you upgrade your monitor.
"IF" you did some light OC'ing (which you should with this option), than the Intel e2140/60 and a p35 mobo would be a smart option too. Since you stated that you don't want to OC, than this option isn't what you want. It would be a good solid option, if you eventually considered it.
Finally to answer your original question, YES the x2 3800 and a AM2+ mobo would be a decent upgrade from your P4 system.
Whew!!! That was a bit too much for such a simple question, I guess. Just needed to get that off my chest, I guess
