No. Never install software you have never installed on an
"existing server". All/any products should be installed on
a test server, not on a production server. Ever.
Oh, and this goes for those of you writing emergency
posts because you directly installed SP2a on a
Production machine! NEVER do that. Always do it
on a test system first!!!
Now, if you were an experienced installer of MS Project
Server, will you install MS Project Server on an IIS unit
that already has MS SharePoint Services on it?
No. I will use a test machine with the exact configuration
to see if it installs.
However, if you never installed MS Project Server ever, then
I would add ana dditional step --- try loading MS Project Server
on a clean system and take notes!
NOTE: Back to the "existing server" --- IIS better not have been
tweaked, or the install will fail... So try it out on a test unit!
So the ulimate answer is, yes it will work but do it
on a test system first. Then do it on the live one...