You really are better off going to a post house that offers standards conversion or a standards conversion service. They have dedicated hardware that does it in real time.
The other way is to find a rental house that will rent you a PAL deck and a "scan converter". If you have a lot of tapes, that may be a cheaper way to go.
If you are in the LA area, go to 
www.411publishing.com/cahners/index.asp. Look under Americas >USA >California  > Equipment & Supplies > Video Equipment & Facilities. 
Here is one place I have rented from. They have always given me good service:
Video Equipment Rentals
912 Ruberta Ave.
Glendale, CA 91201
Tel: (818) 956-1444; (800) 794-1407
Fax: (818) 241-4519
Web: 
www.verrents.com
Email: 
[email protected]
Description: (Video Camera Systems)