Replace grahpics card ThinkCentre S51 (type 8172)?

I got this box like computer ThinkCentre S51 (type 8172)]
http://www-307.ibm.com/pc/support/site.wss/MIGR-58587.html
Can I replace the graphics card for a more suave one? Memory is cheap and i was thinking of making it gaming worthy.

Look here:

http://www-307.ibm.com/pc/support/site.wss/product.do?template=/product.do?template=%2Fproductpage%2Flandingpages%2FproductPageLandingPage.vm&sitestyle=lenovo&brandind=11&familyind=179854&machineind=180051&modelind=0&partnumberind=0&subcategoryind=0&doctypeind=100&doccategoryind=0&operatingsystemind=49980&validate=true

ftp://ftp.software.ibm.com/pc/pccbbs/thinkcentre_pdf/19r0486.pdf ( start at page 143 )

Alternatively, you can go here: http://forums.lenovo.com/...o.com/lnv/

Hope this will start you on your way to get the info!