i got dashcommerce 3.0 working on xp and win 2k server.
install all requirements. (AJAX, MS.NET 2.0 Framework, SQLExpress2005)
install sql2005 express. create db.
Install visual studio (i tested it with 2008 (download the trial version if you dont have) run the .sln once you open in Build solution.
in IIS create new site or virtual dir point it to Web folder in the dashcommerce folder.
open browser goto http://localhost/install/install.aspx
when it ask for db setup for server put "localhost\instance_name" ex. your server name is ECOM and your sql express instance is default then it would be "ECOM\SQLExpress" server name.
you should not experience problems with this setup. The reason i wrote this cause i kinda went nuts trying to run the app but at the end got it working. I got the metal system error too but this solved my problems.
you can download the .zip file extract it pont your iis virtual dir and start the install. Good Luck.