I 'm under considering workflow system to support my project.
Web pages was done by ASP.NET
I 'd look around jBPM and believe this project is flexible and have big community enough to ask :P
Can jBPM task use external forms? Do you have example ?
yes it can use external forms but unfortunately the webservices interface in jbpm3 is not fully finished/polished/etc... The 4.0 release though (upcomming july 1st) will have a rest interface within the console. So you could leverage that.