Simulations...boon or boondoggle?

I have been assigned this year a class in US History for 8th graders. I also teach 4 sections of physical science. My personal goal for this year is to bring in technology whenever possible...as a teaching tool, a learning tool and a tool for expression.

In history, I have found and used simulations that puts kids in the shoes of colonists in Jamestown as well as on board ship. Kids have done fact exploration online and this week are going to start their project that will use iWeb.

In science, however, I have run into some walls. For one, the system blocks many online sites that offer simulations. For another the computers that we use are a mixture of old and new and not all of them can handle the software. Finally, in science, I find that many online sites offer kids little or no chance to make mistakes...many are canned to the extreme...so much so that there are not chances for kids to make errors. The hands-on, using equipment and manipulation, allows for this.

So here is the crux of my question...which is better? Exposing kids to science through technology in a very cookie-cutter way or is the equipment using part best? Are there simulations/sites out there that will do both? What have others of you found?