Below is a link to Xilinx website:
**broken link removed**
Here u can get a better picture of ModelSim XE and ModelSim SE.
As for ISE Foundation and ISE Webpack, the difference is ISE webpack is FREE.
Ok, if something is FREE. Definitely, there are a lot of limitations. Right?
For more info, u can check on Xilinx website or mayb someone out there has an experience using both software can share with us.