It sounds like you're using an integrated graphics chipset. Those are notoriously feeble when compared with using an add-on graphics card. There are a couple of possibilities:
1. Your graphics chipset is simply old and/or incapable of fully supporting some graphics capabilities (particularly 3D features)
2. Your graphics chipset needs driver updates (as was already suggested).
If your PC a branded PC, like Dell, HP, EMachines etc? If so then visit the manufacturers website for driver downloads.
If not then visiting the SIS
website might yield some more up-to-date drivers. (I post this link because it's the first thing I found when searching for "sis 661 fx")
Nevermind, another_commander gave a more definitive answer. Perhaps you could give your old PC a new lease of life by buying a better graphics card. Although I appreciate with somebody who is self-confessed non tech-savvy that might be a daunting prospect.
Oolite: A grOovy Kind of Love