The full installation is 150MB
The patch is 48MB (You shouldn't need this unless you actually get an error saying the client is out of date)
Once it's all installed, it takes up about 240MB of space, it's not much, the game is very light on graphics and SFX, mainly because it's low priority for them as this is a beta, and they're more concerned with code than the appearance, especially since they aren't trying to market the game. It's a free open beta, and they don't want to get TOO much attention