Hi,
If you're talking about this :
http://www.dixons.co.uk/gbuk/compaq-presario-sg3110uk-m-desktop-pc-with-20-monitor-06318503-pdt.html
I'm afraid it's not just "a little" below the specs, as :
1. it doesn't even have a true 3D graphics card. (correct me if I'm wrong, but the ATI mobility HD3000 - which is made for laptops - doesn't offer 3D acceleration, it's more about multimedia and HD videos),
2. it probably has no dedicated memory for display, which means the display memory is taken from the main RAM of the computer,
3. It doesn't have enough memory (minimal requirements for windows seven is 3gb, this computers only has 2gb and a not negligeable amount of this ram will be used for display ...)
I'm very sorry to say that I'm pretty sure this computer won't be able to run SS Extremes correctly, and I believe it won't be able to run it at all ... And it probably won't run other modern 3D games neither.
You can find the minimum requirements for Ship Sim Extremes here :
http://www.shipsim.com/products/shipsimulatorextremes