I am about to film a documentary in PAL format and output it on DVD.Later I would like to market the DVD in countries using the NTSC format.What would be the easiest and cheapest option for conversion.
I use a PC with Premier Pro 1.5 editing program.

Probably depends on what software you're using. On the PC I've heard that Vegas can do this I think. On the Mac the new version of Compressor will do this, but evidently it's really slow. DVfilm Atlantis runs as a small standalone program on both Macs and PC's:

http://www.dvfilm.com/atlantis/

Or if you're using FCP on the Mac you can take a look at Graeme's Standard's Conversions: http://www.nattress.com/standardsConversion.htm

Thanks for the info Boyd,the Atlantis looks like the right tool for the job.

Know where I can get some tips and tricks using the new compressor for this. I tried it and the results were so bad I chose to sell that DVD for the UK and Europe Only and market it in the U.S. as a special import that due to the PAL format will only play on computers.

I just looked at the Atlantis website. the explanation on how the software works sounds impressive. Has anybody tried both Nantress and Atlantis to see which works best?

Both programs have free trial versions that are fully functional. The best approach would be for you to try them yourself and see what you think.

http://www.nattress.com/Products/standardsconversion/demo.htm
http://www.dvfilm.com/atlantis/macversion.htm

I believe that one difference is Atlantis converts your 50i video to pseudo 30p as part of the process whereas Nattress doesn't. I've only used Atlantis to convert NTSC to PAL myself.