There's various 'flavours' of Java depending on what the target device supports. Understanding this makes things a bit easier later on - some platforms don't support floating point for one. I found this out whilst fiddling around porting code for my mobile phone for Bluetooth. J2SE,J2Me....versions etc tell you what is allowed and what is not. The Sun website goes into great detail.

I used Netbeans which needs a lot of ram and cpu performance. 256m on a P3 is a bit sluggish, ok on 512m P4 though.

Like most things, there's a bit of a learning curve to get started, but once over the hump its all much the same as any other language. There's plenty of stuff on the web to get you through. Getting your first program compiled and running is the first battle.