All 3 of those cards are MUCH faster than that x1300pro you have been looking at, and all are under $100.
I would go with the x800gto as you can potentially unlock the other 4 pixel pipelines and have what is basically an x800XL. The only drawback is that it does not have pixel shader 3.0.
If that means a lot to you then its pretty much an even choice between the 7600gs and the x1600xt. Both are graet value at that price.
EDIT! I didn't read the thing about it not being used for games. If it is just being used for video encoding, get the x1600xt because of ATI's AVIVO.
AVIVO also comes with x1300pros, but the x1600xt is MUCH faster than the x1300pro. It's in a different league.
I found an inno 3d 7300gt
Chipset: inno 3d GeForce 7300 GT
Memory: 256mb GDDR3
Core Frequency: 500MHz
Memory Frequency: 1400MHz
Pixel Per Clock: 8
Memory Bus: 128-bit
Max. Resolution: 2560 x 1600
SLI Ready: Yes
Output: 1. Dual-Link DVI | 2. DVI | 3. HDTV
it was only £45 and could run fear on high settings at 1280 x 1024 @ 42fps and bf2 @51fps when on high settings @ 1024 with 4xaa 8xaf which is pretty decent for a cheap card. whats more u could have 2 in sli and then that woul kick some ass (although that wont be in ur buget)
if you know what ur doing a x800gto will when unlocked / oveclocked perform about the same.
the machine won't be used for gaming and would mostly be used for video encoding etc.
i would strongly recommend a dual-core cpu, i have a x2 3800 and video encoding is alot faster. although the 3800 is 2.4ghz and the x2 is only 2x2.0ghz, the are easy to o'c if necessary and run cool(mines idles at 25C on stock cooling)