I would say forget about it. Here's what I tried and my results (posted in another thread a couple weeks ago):
Okay, just for kicks I installed Oblivion onto my laptop, which is:
- Pentium M 1.4ghz
- 512 meg RAM
- GeForce FX-go 5650 w/128meg
- XP Pro w/SP2
Playing at 640x480 with rock bottom settings
I turned EVERYTHING down to the absolute lowest settings possible, and, while the game would technically "run", you couldn't really call it running. It took me forever to just pick the basic guy they give you because it wouldn't register my mouse clicks and the curser was moving at like 1 frame every 3 seconds so I kept overshooting the buttons.
Eventually I got it started and somehow managed to jerkily grab a skull of the ground and toss it over to the table, and it flew through the air in a slow slide show, eventually falling against the table and down to the ground, after about 20 seconds overall, when it should have taken about 2 seconds.
Then I forced the character to meander his choppy self up to the gate to hear the other prisoner rant at me - the game froze for about 15-20 seconds and I thought it was crashed, but then it started again and the guy's audio started, so it turns out it was just my computer pausing to load the audio clip.
That's when I turned it off and uninstalled it. That was just bad.
The lesson is that if you're hoping to get by on less than the minimum specs listed, don't even try, it's impossible. I'm betting that my bottleneck here is the processor, it just can't crunch the physics, the audio, etc. I'm sure the relatively low amount of RAM (and it's probably slow laptop RAM too) doesn't help either.
I would hazard a guess that the game would simply not work at all on the system you mentioned, that it wouldn't start up or maybe even refuse to install.
But for something like $300-$500, keeping your old monitor, you could get a whole new desktop system that would be powerful enough to run it. You could even do it for less if you just got new MB/Proc plus RAM and a new video card.