Can I use three 1GB sodimm pc2-5300 ram sticks in an imac? Is there any specific way that the memory have to be put in, like one 2GB & one 1GB in order for it too work?
There are only two RAM slots, so you'd have to go with a 2 GB stick and a 1 GB stick in order to get the full 3 GB of RAM. 2 GB sticks run $600+ from reliable vendors like OWC and Datamem.
Which iMac, specifically? (CPU and size)
Each of the models has a different RAM regimen.
The CoreDuo ones do not take 2 Gb modules, nor the entry level 17" C2D.
The G5 iMacs similarly have 2 different RAM setups depending on models.