You can look into SQL Server 2005 database mirroring, although for
automatic failover you will still need a witness server.  There are
lesser levels of availability (high protection and high performance
operating modes) you can build with SQL 2005 Database mirroring that
only require 2-Nodes, however the failover is always done manually.  It
is more of a DR solution than an HA solution.  Check out the details
here...

http://www.microsoft.com/technet/prodtechnol/sql/2005/dbmirror.mspx

http://www.databasejournal.com/features/mssql/article.php/3440511

You can look into third party solutions such as Neverfail and
SteelEye's LifeKeeper (my employer) which provide both the replication
for data protection and application/system level protection using just
two servers.  Another benefit of 3rd party clustering is that it will
work fine with Standard versions of Windows and SQL, Enterprise is not
required.

You can request a 30 day free trial from our website at
www.steeleye.com.

David A. Bermingham, MCSE, MCSA:Messaging
Senior Systems Engineer
www.steeleye.com

MNS covers _only_ the quorum. If you want to cluster SQL 2005, you will need
shared storage for the database and transaction logs.

You can use 3rd party software for this, but if you do, then you must depend
on them for your support, too.

Another option you have with SQL 2005 is to use Database Mirroring. See
books online for additional information.