We use the TV-One C2-2355A Scan Converter
http://www.tvone.com/c2-2300a-main.shtml
(more functionality than an ImagePro for about a quarter of the price...)

or the TV-One C27200 Dual Scan Converter
http://www.tvone.com/c2-7200-main.shtml
(Dual channel Scan Converter and switcher / processor)

and also the TV-One 1T-C2-520 DVI to HD-SDI as a simpler (cheaper) option
http://www.tvone.com/1t-c2-520-main.shtml

Simon