Even with good security programs XP is really insecure. Also, I have a VAIO VGN-FE11M which has 1 gb ram and Windows 8 works really good at it. I can play Minecraft without frame issues.
Maybe you have outdated Java. Go to http://www.java.com/download/index.jsp and check if you have the latest java for your system. Also you may have the wrong version(32 bit or 64 bit). And what have you done before this has happened?
