Is 256 MB good for a computer?

Because I can't jump to conclusions on what you are trying to ask, I made some assumptions below:

Assuming you are talking about RAM, it is not enough to run the latest build of Windows or Mac. At least 2 gig is the minimum unless you are using an older OS.

BUT if you are talking about VIDEO RAM, then yes, 258 mb of video ram is enough.

Assuming you are talking about disk space, 258 mb is not enough to handle the latest build of Windows or Mac.