You won't find many desktops in that price-range that could be used for poker and co-opted for Starcraft 2, much less laptops. In fact, outside of VERY cheap netbooks, I doubt you can even find a laptop that fits into an <$300 package. If you can up the price by a smidge you can probably pick up a netbook with something like an Atom n550 (dual core Atom w/ hyperthreading) for in the range of $350+. If you want any modern CPU (i3+) you will need to think in the range of $500+.
