Are these temperatures ok for stock AMDx2 5200?

What do you 'LOAD' your CPU with to get 53°C?! If it's two instances of prime (one for each core) and you're on stock cooler you're OK but if it's something else like a game, they usually don't max out the CPU.

Bad idea; a DVD burn is only like 20% utilization and most games are single core, so they only use 1 core out of 2 in a dual core and even if you had a game to use both the cores, they're more GPU bound than likely to max the CPU out. Download Prime and run two instances of it simultaneously, specifying one for each core; only this way you can get your REAL load temps and REAL idea of the stability of your CPU. Google for it and download it; don't be surprised if your load temps get 3-8°C higher. And don't forget to take RMClock; it's awesome if you have to OC a X2 or single core A64.
EDIT: Make sure you have at least a couple of 80mm fans for intake/exhaust in your case because anything less, will not be enough to provide fresh air for your CPU heatsink to cool well enough.