As you may know, Slash development for the past several years has all been in CVS, with no tarball releases. We may do a tarball at some point, but for now, we recommend installing the most recent R_ tagged code from CVS.
We tag the code with T_ for our own use (on Slashdot, slashcode.com and use.perl.org) and when we feel one of those weekly test builds is stable enough, we also slap an R_ tag on it. A complete list of tags can always be found on sourceforge.net (in the "Show files using tag" menu).
If you are running a site on a very old version of Slash pre-2.2.6, we still recommend that you upgrade to 2.2.6, but the upgrade path beyond that to a recent CVS version will be long and difficult. We recommend you research whether you want to do that.
On the other hand, if you have not already invested a lot of time into a Slash site, we strongly recommend that you begin with the most recent R_ tag.
Today we made a new R_ tag, our version of Slash from January 11, 2006: R_2_5_0_94. This is the most recent since R_2_5_0_74, which dates from June 2005.
The biggest change is CSS, which was implemented just a few weeks after _74. Other changes include reskeys (which largely replace formkeys), and public logtokens (which improve security).
So the current recommended process to build Slash is:
cvs -d:pserver:email@example.com:/cvsroot/slashcode login
(password is blank)
cvs -d:pserver:firstname.lastname@example.org:/cvsroot/slashcode co -P -r R_2_5_0_94 slash
In the slash directory created, read the INSTALL file (the entire file, especially REQUIREMENTS). Then, if you still want to install Slash, follow the instructions in that file carefully!