I am assuming you're talking about RAM. These are the minimum requirements for WC3:

400 MHz Pentium II or equivalent, or a 400 MHz G3 processor or better.
Windows 98, Windows ME, Windows 2000, or Windows XP.
128 MB of RAM.
A hard drive with at least 550 MB of free space.

This is the bare minimun for the game to even run. My old computer barely met these requirements when WC3 came out and the game ran terrible. Load times were awful and the graphics were set all the way down and it still was choppy (that's more the graphics card however). Obviously the requirements for SC2 will be higher than this. How much no one knows yet. But I'm guessing at least 256MB will be the minimum. Meaning while it could run it would be terribly slow. A memory upgrade would be relatively cheap and definitely worth it. If you're running XP with only 256MB you'll notice a nice differene after an upgrade.