Xilinx and Altera Modelsim on the same PC?

Hi all,

I've been using Altera parts and tools for quite a while and currently
have Quartus-II 4.1 on my PC along with the Modelsim-Altera 5.8c.

Now I need to do a Virtex-II design so I obviously need to put some
Xilinx software on the PC.  I've used Xilinx devices and tools before
(not the newest ISE, but a pretty old version of Foundation I think
and the earlier Webpacks).

Anyway, I've installed the newest version of the Webpack software
(looks like I remember it for the most part) to use at least
initially, but I hesitated on installing the Xilinx Modelsim.  If I
install the Xilinx modelsim along with the Altera-Modelsim am I going
to have all kinds of conflicts?  I've never had both on the same PC. 
Right now the Modelsim-Altera is working well integrated into Quartus
to fire up a timing simulation immediately after fitting so I'd hate
to mess something up.

I'd imagine I could do behavioral simulation of the core VHDL files
for the Virtex project in the Modelsim-Altera fine, I just figure I'll
have to have the Xilinx version to do any kind of post-place and route
timing simulation for the Virtex part.  Is this correct?  Does anyone
know the best way to go about this?  Thanks.

Sean