Well to gauge how much pain will be involved..
Do you use Dynamic Properties tasks?
Do you use ActiveX Scripting?
Do you use UDL files?
If you do then it is more painful.
http://pragmaticworks.com/Products/Business-Intelligence/DTSxChange/
Has some good information. I have seen their tool demonstrated but I am always wary when they don't list pricing on the website. but either way they do have some good information.
http://pragmaticworks.com/Support/FAQ/DTS-SSIS-Package-Migration-Conversion-FAQ.aspx
CEWII