Unable to move installers from desktop to folder

Just wondering if anyone knows why on OS X Tiger when after you download certain items to the desktop and install them (such as msn messenger, gmail notifier and other various), you are unable to move them (the installers that is) from the desktop to a folder? It seems to only create an alias into the folder you try and move it to. I've checked to see if the item is locked, but doesn't appear to be. This has me stumped.

Also with programs such as msn, once installed leaves another constant icon on the desktop which dissapears everytime the computer restarts resulting in having to open the .dmg file everytime I need to use msn. The option of keeping an alias on the dock for msn is impossible too.

Is there something I'm missing?

Any help would be appreciated.

Cheers

Not sure about the first part, but the second part is that you don't have the application installed yet. What you have is what I called a virtual disk. Drag a copy of the application from the white disk icon to your application folder. Once that is done, you will have installed the application. Then you will not need the .dmg file or the virtual disk.

RMAN got the second part well. For the first part open up Macintosh HD > Applications > Utilities > Disk Utility. Click your hard drive and then "Repair Disk Permissions". When it is done your problem should be solved.

Hey RMAN, I tried doing as you said but it's still creating the "virtual disk" concept on my desktop. When I try to move the white disk icon into the applications folder it simply creates an alias, even after Benjamindaines's suggestion to "Repair Disk Permissions." So I'm not sure where to go from here.

Any other suggestions? Has anyone else ever come across this?

Something to consider...
Create a downloads folder in your home folder. Tell everything to put downloaded items there (Safari, etc). OS X treats the desktop differently than other folders.

Why drag the "white disk icon" to the Applications folder? Double-click on it..A disk image will mount in the FInder. Drag or install the application itself to the Applications folder, then unmount the image and trash it or save it somewhere else (I burn mine to CD if it's something I want to keep).

Ok I figured it out and basically what everyone was saying was just about right but instead of dragging the white disk icon into the Applications folder, you double click on it. Opening up a window with the MSN icon. You then drag that icon into the Applications folder and you're all done.

Something simple which took me awhile to get my head around. My brain works slowly sometimes *sigh*.

Anyway, thank you to everyone who posted and provided some very useful advise. Much appreciated.

Cheers