Well the answer is yes and know If you do indeed get different memory they might play together and they might not. Through past experience this is the case. If they do they will run at the slower of the two speeds, if they don't you have spent $ for just the 512 which should run ok on your machine, maybe :). I hope this helps and I don't seem like an idiot but this is just the way it works with memory. SO for my $ I would match the memory.
Sorry thats a pun...my query is about memory, i currently have 1 stick of memory in my machine - Kingston 256mb 333Mhz DDR PC2700 - What i'm confused about is the 333mnz and the PC2700 parts, i'm looking for more memory but i'm not sure if i need to buy the same i.e PC2700 and 333mhz, can i mix and match? for instance the one i'm looking at is 512mb 400Mhz PC3200, will this have any effect.
Rnning: P4 2.4Gb and XP Pro.