Dual booting linux
 

Is it possible to dual boot linux.
I want to install Slackware and RH 9 on the same HDD.

Sure - just like dual booting any other except that they can share swap partitions - you can even sorta blend them if you know what you're doing. Slack should go right on there.

I have a friend who at one point was booting Win98, Win2000, BeOS, Mandrake, Caldera, RedHat, and a couple other operating systems on the same machine. So yes, it's quite possible :)

But as digiot says, it may be hard to mix and match partitions with them... i.e., it's tricky to let two of them share the same /usr partition (though you may be able to share /home without much trouble).