I've recently had this question asked about InfoPath/SP licensing: "What licenses will my company need to use InfoPath forms with SharePoint".
If you are going to use InfoPath Forms on WSS/MSS you are going to need the correct licensing - you will need the MS Office Forms Server + CALS for your internal employees and if shared with external persons, you will need the MS Office Forms Server for Internet Sites. You will want to also check other licensing schemes for MOSS/WSS that will apply differently to internal/external usage.
Here's the scoop from the MS office SharePoint site:
Microsoft Office Forms Server 2007
Per Server and Client access licensing. For each server, or each server in a farm, a valid server license must be purchased. For each client accessing Office Forms Server 2007, a Forms CAL must be purchased.
Microsoft Office Forms Server 2007 for Internet sites.
Per Server licensing only. Office Forms Server 2007 for Internet sites is for running forms solutions on extranet and Internet sites and should not be used for forms solutions for internal use only (for example, a forms solution on your corporate intranet)
Full details here at the
Office SharePoint FAQs