While there are a few nice features in InfoPath 2007 like the design checker,
improved offline capabilities, better integration with Outlook 2007, and a
new object model that uses the System.XML namespace like in .NET, a major
effort has been put into its browser capabilites. So if you can somehow
justify needing or wanting browser forms you might have a reason to buy
InfoPath 2007. But then you'll also have to buy a package deal, since you
cannot use browser forms with SharePoint 2003. You'll need Forms Server. And
if I were you, I would go for SharePoint 2007 instead of Forms Server alone,
since SharePoint 2007 contains many enterprise features your organization
could make good use of like search, workflow, content management, document &
records management, Excel services, etc., in addition to Forms Services. Pay
careful attention to the different editions, though, since features differ
per edition. I guess you'll need to look ahead 3-5 years and foresee in which
areas your organization might/could grow to upgrade to Office 2007.

Hope this helps.
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S.Y.M. Wong-A-Ton