Actually 7.0 didn't use Xorg, it used Xfree86.
X in both cases is the X Window system, a graphical frontend for unix, essentially.
Savage is a company, SiS is a company, both made onboard graphics. SiS makes more as well, savage only makes onboard graphics.
Upgrading from SuSE 7.0 to SuSE 10 would be more like Win98se(or even WinME) to WinXP. So long as your computer can handle the requirements, you can easily do SuSE 10. If they are too low, for instance you have an inadequate ram amount, you cannot use SuSE 10. If you meet the reqs, it will run just fine.