If you just want to do this for a hobby, say just have something posted on youtube. And for personal learning:
You can get by with a minimum of a 2 gigs of ram. Filespace? Depends on how big your projects files you expect to keep, how you will do your backups (dvds?, external drives?, online backup?), physical hard drive space required by your softwares, etc.
If you're just going to do this for giggles for now you can get by with 30-50 gigs of free hd space on your animating laptop or desktop. And just archive files as needed on dvds. The .flv files that youtube accepts is very low file-size wise so if you expect to do something like 3-5 seconds of animation every 4-6 months you can just get a relatively inexpensive pre-made computer (undera grand and including a monitor) for your animation use. Important thing you should make sure of besides ram is that the graphics card works well with whatever app you'll use for animation - especially if you do 3d.
You can even get a system first and try out demos of your animation apps (flash, 3d apps, etc) and see if they run okay on your specs before buying them. This way you have a better clue whether to add more ram and anticipate data storage requirements.
If you know what you're doing, money is not a problem and you must output everything in high def, sure go for terabyte drives, multi-cores, 64-bit os/tools, and as much ram as you can stuff your machine.