Windows 7 (at least i have a machine that has Windows 7 that) does support multitouch. However, most traditional PCs (at this time) do not support multitouch. You may want to go with iOS, Android, or Windows Phone, or wait until Windows 8 comes out.
uniTUIO will get you what you need until Unity adds much needed built-in support. You will need to register to gain access to the uniTUIO side to download it but it should be open for development use. It was a little bit of a pain to get going with but we were able to build an awesome game for a giant 12 point touch screen with it.
Grepping the source code of Unity 3.4.1 indicates that Windows 7’s multi-touch/gesture support is not currently used. The touchscreen support mentioned is a bit misleading - it appears to be single input mouse emulated only.
Unity 3.5 appears to handle device hotswapping, but does not appear to add any Windows 7 Touch API support.