If an application locked up under a previous version of Windows, then there was nothing you could do about it. A new Windows 7 feature, however, can not only explain the problem, but may get your program working again without any loss of data.
When the lockup occurs, click on the Start button and type in 'resmon.exe' to launch the Resource Monitor. Click on the CPU tab and find the frozen process (it should be highlighted in red). Right-click on it and select 'Analyze Wait Chain'. If you see at least two processes in the list, then the lowest, at the end of the tree, is the one holding up your program. If it's not a vital Windows component, or anything else critical, then save any work in other open applications, check the box next to this process, click 'End Process', and your locked-up program will often spring back to life.