Scan converters convert the computer RGB signal to another format; NTSC composite or Y/C instead of the video card doing it which usually results in a better finished product. It is external to the computer, NO software or changes are needed to the computer or the screen resolution which is the big advantage! The downside is cost. Depending on which one, it ranges to about what a video card with the feature would cost to over $2,000 (if you wanted/could afford a professional model) Figure around $150 to $300 for a mid priced model.
Try here: (knock yourself out)
http://www.tvone.com/scanconpage.shtml
http://www.hallresearch.com/
http://www.analogway.com/z/prod4.htm
http://www.focusinfo.com/products/b_tview_con.htm
http://www.commspecial.com/products.htm
http://www.aitech.com/retail.htm
https://secure2.nexternal.com/shared...unt2=541450142
and here (most popular I believe):
http://www.aver.com/products/comptv.shtml