Having done things like this myself, I would recommend just buying a heat gun. The oven method can work, but its excessive and its really not healthy to directly expose your cooking appliance to whatever comes out of the board when heated. Anything made of plastic will melt unless it is a high temperature plastic meant to endure this method of soldering (like the plastic packaging on a chip for example... that'd be fine).

would you be able to put it inside something like an airtight dish while in the oven to prevent anything happening to the oven itself?
If the graphics card is dead already, there really isn't risk of making it worse.

Does, by any chance, Q13 mosfet on 7600GS heat up to the point where you can't hold your fingers on it? Also, try testing it in older AGP 4x motherboard, it helps sometimes.

This generation of cards has several problems that causes failures mainly thermal death and rot caps while the other can't be fixed short of either buying another card or replacing the gpu which not very many people have the tools on hand to do. Oven baking can "fix" a card if the broken joint is the crappy tin balls between the gpu substrate and the rest of the card. Look into "nvidia bump gate" then you will understand why just baking a card won't really fix it unless said as above because when the fault occurs between the gpu die and the substrate as it is almost always fatal. The same goes for faulty VRM where a failed mosfet can allow unregulated voltage from the psu to the core killing it beyond repair which does plague modern cards a lot.

I might have Asus A7V-133 duron pc somewhere in storage, so I might try the nvidia cards with that before cooking them.
It is always matter of if you are going to throw them away, you might as well try something (like baking it). You can't make broken graphics card any worse.

Chances are pretty good that your cards just need to be recapped. I have a Geforce FX5500 AGP and a 6200 AGP that both need to be recapped. I've had to replace VRM caps on pretty much every Socket 478 and 462 motherboard I own or have owned. I'm pretty sure if you change out the caps they'll run fine. My FX5500 works fine for a few minutes, sometimes it's gone hours, but the moment you run anything 3D it craps out and the screen locks hard or it will go blank. The 6200 starting acting up more recently but a quick look at the card and I have a bulging cap on it.