I did some hunting on this system, it is using its onboard video for graphics. How capable this is for 3D graphics I am checking on, but you would be better to install one of the popular 3d vidcards from NVidia or ATI, MSTS should run fine on an NVidia 5500. Visit a local computer store.
price for an inexpensive card can be around 70 bucks and work fine. High end cards run around 200-300 dollars, but it will perform extremely well.
it looks like this system was not made for 3D accelleration.
http://www.intel.com/products/chipsets/845gv/index.htm
http://www.pcstats.com/articleview.cfm?articleid=1610&page=4
adding a 3D card means it has to use a PCI slot as it has no AGP or PCI-E slot. a PCI vidcard might still be available but you will have to check around.
maybe you can get one at newegg
http://www.newegg.com/
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=2010380048+1069609642&name=PCI
a few selections.
Lloyd E.