The theoretical limit (what it was made for) is 512 mb for Windows 98, however there are work arounds if you install more than that to keep windows from crashing. So in practice you can easily have 512mb with win 98 and over 512mb if you don\'t mind editing some files manually.
Oh and the above poster is right, try to keep the same speed ram in your system ( as a bonus you can try to match no only the bandwith but also CAS latencies). Examples are Cas2 Cas2.5 and Cas3. All things being equal, use the fastest memory your MB will support with the lowest CAS latency.
Lastly newer memory (PC100 on up) was designed to be backwards compatible. So if you toss PC2700 memory in a mb that can use pc2100 at best, the PC2700 will work at the lower speed.
Forgot to add! Some motherboards will interlace memory. This only works if you\'re using identical memroy and can definetly provide a performance boost. Also there is an issue about the most memory you can effectively cache and this will vary according to your L2 (or L3) cache. Modern systems usually can cache as much RAM as your mobo can handle, however you still may want to check with your motherboard manufacturer to see if you are affected by this. (One such example is the FIC 503+, It can hold 512mb, but can effectively cache 256mb - so the upper ram doesn\'t perform as well. Note that this is the rare exception to the rule).
