If you use lot of evaluation/trial Microsoft software and had difficulty in locating the link to evaluation software, you can bookmark this link: TechNet Evaluation Center.
TechNet Evaluation Center has downloadable beta and trial software under following categories:
Evaluation copy of Microsoft Office SharePoint Server 2007 can be downloaded here.
There is TechNet Plus also which you can subscribe to. Please check the TechNet Plus Subscriptions website for subscription levels, langauges, media types and pricing for your region.