Help Needed. Changing from PC to Imac

Well, i'm on the market for an imac G5. I just wanna know if the ram in my current PC would fit in the Imac? And for anyone whos got an imac... should i go for the 20" or 17" monitor? I'm a design student and need it to run photoshop CS and a couple of 3d applications. Does it handle these programs well.

Thanks.

Thanks for the reply. What type of ram do imacs take? I think i've got DDR in my PC. And would it be able to handle photoshop and rhino 3d well?

Thanks again.