If you have converted an IC motorcycle to electric, you can use form 8910 to obtain a 10% tax reimbursement - but read the form instructions and qualifications thoroughly before you complete it.
The form to use for the purchase of a new plug-in motorcycle is form 8834. This credit reimburses you for 10% of the cost of your new electric motorcycle, up to a maximum of $2,500. To qualify, the motorcycle must be road legal, registered with the state and placed in service during 2010 (or your tax year), and have a battery pack of 2.5 kW or greater if the vehicle has two or three wheels. This other qualification has got me stumped: "The vehicle must also be a vehicle with 2 or 3 wheels that, according to the manufacturer, has a loaded weight of less than 14,000 pounds"!
These comments were provided by me from reading the IRS instructions for form 8834. Since I have no accounting or tax preparation experience, don't take my word for any of this information. But at least it should get you going in the right direction. Have fun filling out the form. It is really a relatively easy form to complete.