SLi?
Is that not when you have 2 Graphics card hooked in tandem!
So yes, you would need to change the MB.
If you intend using the same processor, then check the new MB it will be able to manage it, also would you be able to upgrade the processor at a later date, if you fitted your existing processor now.
Also will it take the same memory you already have.
>> and if I do can anyone tell me what information I need to be able to change the Board.
All of the above, possibly someone else might throw some light on the matter.
Other than that, a bit of patience, most if not all of the connections are plug connectors and "most" will only fit in the correct socket. (but check first, better to be safe than sorry)
SATA, Esata or IDE drives?
And will your power supply (PSU) unit take it
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I have rebuilt one or two old computers so know the feeling of doing it yourself, but nowadays with the price of complete ready-made units you will not be saving very much by the time you have finished.
"Plus no 3 year guarantee" as with a new one.