As regards what will fit, all DDR RAM fits into a DDR slot, though obviously there are other factors which decide whether or not a particular DDR module will work.
The sticker seems to be a good start. You need PC2100 DDR modules, though many motherbaords designed for PC2100 can also use higher speed modules (allbeit at the slower speed performance-wise) which is useful to know when one type becomes scarce.
But you also need to know whether the RAM needs to be the 'buffered' or 'unbuffered' type, and whether it should have error-correction (ECC) or not (non-ECC). You also need to know how much RAM each memory slot supports, since it's pointless buying a 1Gb module if your slots can only address 512Mb each.
I've had so many disappointments with incompatible RAM (even though it was same speed as existing RAM) that I now go online to
http://www.crucial.com and use their 'system scan' tool which can tell you in seconds what modules are compatible with your system, and then show you what they have to offer based on the scan.
Linear Mode
