Windows 7 will run just fine on a Machine with as little as 1GB of ram so long as it has a decent graphics setup. 2GB+ will run great for most people, 4GB is excellent....I use 6GB.....my brother uses 16GB.
Freezing is most likely a heat issue, or failing hardware. I'll assume by its 1.25GB of ram that its not exactly new.
Issues:
-Dusty/dirty = overheating
-Failing hardware (Ram, or Hard drive)
-Software error (less likely)
-Messed up attached peripherals
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