You didn't say whether you have other servers already. If this is a FIRST server (or even if it isn't), take a hard look at Windows Small Business Server 2003. You can set up a box with Server 2003, Exchange, (and, if you want, ISA 2004 and SQL 2000) in a matter of hours. The hardest part is joining the client PCs to the Domain, but if you know the tricks, that can be done in about fifteen minutes per client if the clients already have XP Pro or Windows 2000.
SBS automatically installs and configures Outlook 2003 on the client PCs. SBS 2003 also gives you automated backups of the entire Server (including Exchange) and automated Server status reports that it emails you every morning.
The only thing is....I'd recommend planning on doing your first install TWICE. Once to learn the tricks. Then, re-install it for the real install. If you buy a Dell OEM install, you'll probably want to re-install SBS anyway....they really don't provide enough space on the the system partition for future upgrades.