There are reports that iPhone OS 3.2 (first used on the iPad) will support file downloads, see
Confirmed: iPhone OS 3.2 has support for video calling, file downloads, and SMS. This will presumably also be eventually available on the iPod Touch.
If you strip the DRM from the ePub ebooks, then Stanza Desktop or Calibre can setup a service on your PC to transfer them to your Touch. Another option is
Txtr iPhone app - Adobe DRM, over the air downloads, and more. This now works with DRMed ePubs.