go to www.redhat.com , u can dl a free version, 4cd total.
there're serval linux distribution, it's hard to say which one is best, it's really depends on ur need.
If you want to study unix, just install linux ,that's ok.It is also one type of unix.
要使WINDOW98与UNIX操作系统怎样装在同一台电脑里,你要设置不同的分区,我觉得你既然用PC,最好用linux,solaris的X86不太好用,SCO UNIX在这边根本没人用.