Thanks for the links. I took a quick look at the tinycad website, but couldn't work out whether the package supports schematic-based hierarchical design - can you clarify this? Incidentally, the best* free SPICE-like simulation package that I have come across is LTSpice**. It has its own schematic capture package, but you may prefer to use one you are more familiar with.
*For reliability of simulation without sacrificing accuracy.
**Linear Technology will even support the product if you are using it to design a product that uses their own parts - but I've not (yet?) found support to be needed.