If i have a motherboard that supports DDR memory, am i able to plug my old PC133 SDRAM dimms into it?
more specifically - will it work if i plug them in 
Yes.
No
It depends:D
gee, what a gripping argument this is so far! The chap at the shop where I just bought my motherboard (after i posted the OP) also said no.
However, I believe it is possible to get a motherboard that can support both types (but i don’t trust these!)
thanks for the help
Seriously, some MBs support both memory types and some don’t . Your manual should clue you in. If you have a fairly new and fast processor you should not be using SDRAM anyway, even if you could, as this will tend to throttle performance.
If the form factor of the memory is the same it will work. DDR RAM merely tranfers data on the risining AND falling edge of the clock cycle thus doubling data throughput. The system is quite capable of reading only the rising edge of SDRAM.
In fact, I believe you can mix DDR and SDRAM chips in the SAME system. The DDR RAM will merely function as regular SDRAM in this case so it’s a waste but you could do it if you wanted to for some reason.
I know that, but the problem is that my old motherboard (sdram-only) is kaput, and money is limited, so if I can save money by plugging SDRAM into a DDR board, I will do so.
It’s all irrelevant now, as the board I ended up getting was another SDRAM-only…
that ‘i know that’ was directed at astro, BTW - i didn’t know whack’s info - so thanks!