Modelsim Installation - previous install not detected

Did anyone figure out a workaround for this? I'm considering purchase of Modelsim, and wanted

to get a feel for how useful it is before plunking down $1000-ish dollars. My installation environment is

CentOS 6.2 running inside a VMware VM, with a fresh install of Quartus 11.1sp2. The modelsim

installer starts, and eventually admonishes me for "You must install the service pack...", with the

installer pointed at the 11.1sp2 quartus install directory. Any idea what the installer is actually

testing for? Maybe a license file from a licensed version of Quartus?

So I'm in a catch-22 situation - I assume I can't get support out of Altera because I'm using

webpack, but I'm ready to order modelsim, if I can establish that it works at all on Linux.