You can also tell by finding the model number of your motherboard and searching for the specifications.
You can also tell by opening the computer and looking at the motherboard. In this picture, the top slot is AGP. The bottom slots are both PCI. [Link](Mouse over link to see full location)
AGP slots are almost always that brownish color.
If you have any empty PCI, PCI Express x16, or AGP slots, then you can install a video card. AGP and PCI Express x16 are best. AGP is slightly faster than PCI-e, but PCI-e is more common.
After you figure out the expansion slot to use, just buy a video card for that slot. Any recent card will run Second Life. Below I list some good, low-cost ones. Also, if your computer is not a tower, you may need low-profile card instead.
Attention: NOTHING on this site may be reproduced in any fashion whatsoever without explicit consent (in writing) of the owner of said material, unless otherwise stated on the page where the content originated. Search engines are free to index and cache our content. Users who post their account names or personal information in their questions have no expectation of privacy beyond that point for anything they disclose. Questions are otherwise considered anonymous to the general public.