You DO get problems if you mod or tweak your Retail install, and then install SCP over that... Retail, you have to put stuff in the root dir or data subdir to mod. SCP has the mod feature for that. But, if you have the CDs, uninstall everything, re-install RETAIL from the CDs, and then install SCP, preferrably after copying the .mves from the disks, as I point out in my walkthrough (Turey's Installer link in my siggy).
If you don't have the retail disks and/or can't figure out how to replace that one file in Collussus that needs replacing (kara knows which one), then just google this:
prototype24 freespace2 torrent
You'll get a result like
this one.
You can get a decent Bittorrent client
here (get the Installation program, not the standalone, unless you're comfortable with torrents, in which case, I shouldn't have to be telling you this.)
Now, install your Bittorrent client (uTorrent), then get prototype24's torrent mentioned above. Then, Google up:
virtual clonedrive
and you get
thisInstall that, double click on the FS2 .iso for disk 1 (after it's done torrenting, obviously!!), and install. When it asks for disk 2, hit your Windows key on the keyboard (or Ctrl+Esc if you don't have a Windows key), and open Run, type in "explorer" and hit enter. Find your protoype24 download again, double-click on disk 2's iso file. go back to the installer, hit next. Do the same for disk 3. Now, copy the .mve's off of the FS2 disks, as seen in my walkthrough. Next, if you have the FS1 .mve's (on the FS1 CD), copy those. NOW, Install SCP to THE SAME FOLDER AS YOU INSTALLED RETAIL FS2 TO.
I do hope that's clear enough!!