Software Installation Issues

Question

I recently had a new boot hard drive installed in my G5. OS X 10.5.8 was reinstalled on the new drive and all my software and settings was transferred to the new HD using Migration Assistant. After that I found that many of my programmes didn't work properly (particularly Abobe CS3 programmes like Photoshop etc) so I needed to do fresh installs for those affected.
Recently, I've noticed that when I try and install a new programme (by dragging its Icon to the Applications folder after downloading a DMG), a message is displayed saying "the item (name of programme) can't be moved because "Applications" can't be modified." The message has a button called "Authenticate." Clicking on this allows the installation to proceed. Then once the installation has been completed, another message is displayed asking me to input my administrator password.
I also get issues when installing software, ie sometimes I need to do it several times before the software works properly (this occurred recently with Toast 10).
When installing software, I used to be only asked to input my admin password before a programme was installed and I was never asked to authenticate anything.
I have tried repairing permissions.

Answer 1

Apologies, I posted the previous answer to your question by accident before I had finished typing: there doesn't appear to be a facility to edit posts once posted. My answer should have read:
Permissions on my applications take the form:
Most apps System: R&W; Admin: R&W: Everyone: R only
Adobe CS3 Pad (Me): R&W; Admin: R&W: Everyone: R only
One or two apps Pad (Me): R&W; Unknown: R only, Everyone: R only
The Applications folder and the System Folder have the following Permissions:
Applications System: R&W: Wheel: R only: Everyone: R only
System System: R&W: Wheel: R only: Everyone: R only
The Library and Users Folders have the following Permissions:
Library System: R&W: Admin: R&W: Everyone: R only
Users System: R&W; Admin: R only: Everyone: R only
Wheel is shown with a two person icon in the Info Window for the Applications folder, the same as Admin. I don't have a user called Wheel on my System. I am the only user. However, the person who installed the new boot hard drive and reinstalled OS X did create a new admin user when he did this. I added myself as Administrator afterwards and then deleted the user created by the engineer (I was told to do this).
As the Permissions on the actual applications seem to be as they should be, is there a reason why I shouldn't delete the User: Wheel from the Applications folder permissions and add either Admin or myself to the permissions list and set this for Read & Write? If this is OK should I also do this for the System folder?
Thanks for your answers so far.