This is a known issue that I discovered this morning.
In my company we are using Windows Sharepoint Services 3.0 with Windows 2008.
The clients have windows XP SP3 with Office 2003 SP3.
The browser is Internet Explorer 7.0.
Some clients have also Office 2007 or some part of it or some compatibility pack.
When they: open a document, edit a document, check-in, check-out, Internet Explorer crashes.
To solve the problem, Microsoft has realized a KB which must be downloaded here:
This solved my issue in the network.