On the other thread you talk about things not uploading properly...
I installed mambo in an ibay also. The thing to watch out for with this (or any php web site on sme) is if you are editing/uploading files with a secure ftp client, or somehow that maybe you unknowingly changed the owner of some files/directories to root.
For an ibay I usually create a group first that will have access to it, put admin and whoever else in that group and the ibay permissions set to write=group, read=group. If things get screwed up, you can just go into the server manager, set the read/write options to something else temporarily and then change it back and it will reset the ownership properly for all files and folders.
I never had to update GD to make it work.