Some of the new features include the following:
a gorgeous and easy to use interface,
a re-engineered turbo-charged download engine,
a central database to manage all your downloads, uploads, and file transfers,
a built-in FTP client (with SSL) that satisfies the basic FTP needs of most users,
Full WEBDAV support and integration,
Full WEBDAV-SSL support and integration,
Encrypted P2P file sharing,
a powerful utility for downloading web content for offline viewing,
Full .Mac iDisk integration,
auto-resuming file transfers anywhere, anytime,
unlimited UNDOs throughout the entire application,
smart folder technology,
and much more! 

Speed Download 5 is a universal binary providing top performance on both PPC and Intel Macs.

WHATS NEW Version 5.0.7:
- New: Optimized for Mac OS X 10.5.5.
- New: AFP integration and support.
- Fixed: Various FTP issues.
- Updated: Tweaked WEBDAV connectivity for better performance and vaster compatibility.
- Updated: Many under the hood improvements to accommodate for all the changes.

REQUIREMENTS 
Mac OS X 10.4.11 or later