This should get you started:
http://www.insimenator.org/showthread.php?t=8821Run the hack detection utility and see if it finds any conflicts.
http://www.simwardrobe.comIf it finds any conflicts, run the sims2 pack clean installer. In the top left where it says "choose directory", highlight "downloads". It'll fire up and start listng all files in your downloads folder. Once it's done listing your files, hit the Type button on top of the columns. This sorts your downloads by type. Anything highlighted in pink is a duplicate file and can be removed by right clicking the item and selecting remove. Items highlighted in red are global hacks. The clean installer won't highlight all of them but does a good job of showing most of them. Items labelled as "game objects" may also have hacks or mods built into them. Back to the conflicts: if the detection utility finds conflicts, find them in the clean installer, right click them, and choose "disable". This will leave them in your game but the game won't use them. Run the conflict detector again to see if it clears up the problem.
Edit: It's also safe to remove any items llisted as "empty package" in the clean installer.