Come 2008, you may not need to convert, as Toyota engineers have leaked that the next Prius should have a 9 mile AER (all-electric-range) from plugging-in.

It may actually be cheaper to trade in your '04/'05 Prius for a new '08 Prius than go for a Hymotion or Edrive conversion.

http://mysite.wanadoo-members.co.uk/ecotech/ecot.htm