Only 512MB of RAM is way too low to run SH4 under any flavor of windoze. You need more memory and a better video card. Going to a minimum of 2gb of ram will drastically speed up Windows and cause SH4 to run much smoother.
I know people have run SH4 with the 9800, but don't know about the 9600.
Try the memory first.
As for buying a new computer, if you do, request XP, not Vista with it.
Depending on your system, you should be able to get a 2GB matched pair of memory sticks for just under $100 with good shopping. I got my Super Talent DDR2800 in a matched set from newegg for $79, and this is 4-4-2-8 memory with heat spreaders.
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"There are only two types of ships- submarines...... and targets" Unknown
"you wouldn't catch me on a ship that deliberately sinks itself"- comment to me from a surface sailor. 
System:
AMD 6300 3.5 GHz | 32GB DDR3 | SATA 300 320GB HD, SATA III 1TB HD, SATA III 1.TB HD | ASUS Sonar DS sound card
NVIDIA 1660 Super OC | Windows 10
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