It should always say "ECC ram" or whatever when its ECC, if it doesnt say ecc or non-ecc then it will mean its not ECC ram. As far as i know if you got some ECC ram and stuck it in a board that doesnt support it it wont work at all.

ECC refers to Error checking code (actually there are several ways it is referred to but they mean the same). Rather than just checking the parity to make sure that the bits transferred are correct ECC allows for actual correction on the fly without a resend if transfer is defective. Neat feature, but it can increase latency. For some this is too high a price to pay. Actually, from what I read this circuitry was included originally not to assure truer transfer but to allow cheaper media material to have the same dependability as more expensive grade media.
 
To do this the memory has to have an ECC circuit and the BIOS has to recognize that it can or wants to recognize ECC as the error checking protocol. The first is built into the memory module. The second (BIOS) is set by you. Some motherboards have two correction modes - Parity and ECC. If you disable Parity, it should disable ECC also. You could enable Parity and disable ECC if your BIOS allows. Anyways, disabling Parity should let you run ECC ram or non ECC ram.

wow i didnt know you could do that

To expand on Sampson's post, the desire to use ECC is really limited to certain functions. Mostly, you see this in database servers with large amounts of RAM that tend to keep most of the memory used. Also, I am under the impression that you can't mix ECC and non-ECC memory even if the motherboard supports it. Now, whether the effect ranges from simply disabling the ECC functionality all the way to not booting at all would depend on the components.

You're right, clutch. Mixing them is very problematic. Further, because ECC and the quality of the material may go hand in hand, you can be opening yourself up to some serious memory errors.
 
On the other hand, when the motherboard says it can support non-ECC memory, the next step is to get memory from those manufacturers who are noted for quality ram. "Generic" ram with the ECC specification may be an admission of a lower grade media which performs acceptably only with ECC enabled

Now a new question. Memory says rated 2.5-3-3 What does that actually mean?

They're timings for the memory at the rated speed. The lower, the better. I believe the first one is the CAS latency, not sure about the other two. If you're leaving stuff at stock speeds and not tweaking the memory settings, that'll be just dandy.

While DDR memory works a little differently than SDram in that it does things that are not strictly on a clock cycle, the same kind of shorthand is used. What these numbers refer to is the delay in filling the memory block with data. This is often called CAS latency. Think of the memory as a big table with columns and rows that have to be filled in so there has to be time between the rows being filled in (RAS) and the columns being filled in (CAS), the time to switch between memory banks, and the time to prepare for output.
What do the numbers actually mean? They are shorthand for the speed of the memory. The lower the CAS latency, the faster the memory. CL2 is faster than CL2.5 (your memory) which is faster than CL3. The other numbers are probably the RAS to CAS Delay and the RAS precharge. Given I've only seen the PC-2700 at 2.5, you have some very fast memory.
Depending on the Bios of your motherboard you can make a number of adjustments to run, for example, CL3,3,3 ram at CL2,2,2. Some motherboards can make as many as four or five adjustments. This is a kind of overclocking without messing with the FSB.
Hope this helps.