Some older PCs I have a) can only take 512 MB of RAM total and b) can't take modern SDRAM. This means I can't just go to the computer shop and buy two 256 MB SDRAM sticks -- instead I have to find a pair from someone else who bought them a few years earlier.
This blog post is here to confirm to anybody who cares that the Dell Inspiron 2500 is not like those PCs. It has the 512 MB limit, but you can just buy a pair of modern 256MB PC133 144-pin SODIMMs, drop them in, and they will work. At least, it worked this afternoon on my girlfriend's Inspiron with a pair of 256MB PC133 SODIMMs from Super Cheap PC.
(Oddly, memory in Japan seems to cost about five times as much as memory in NZ; we were quoted about 23000 yen [US$220] for each 256 MB stick, so I waited until we got back home and paid NZ$57.50 [US$40] instead. Or maybe Bic Camera just has terrible memory prices - I didn't venture in to Akihabara or anything.)