|Exceed on Demand allows you to define mapping of each your ALT keys to either Windows or your X server. By default, left ALT is sent to Windows, left ALT is sent to X. You can edit the settings by going editing your Xconfig file with the Xconfig Manager. Under the Input tab, there is a setting "Windows Modifier Behavior" where you can send both ALT to WIndows or X, or split the actions up.|
I would suggest keeping one ALT key available for Windows, if you don't use it as frequenly, just swap the setting to left ALT for X, right ALT for Windows.