After creating a pet, I like merged it to an existing family and went into the lot and saved. When I try to click on the lot, the game completely freezes on me. I removed most, but all the incompatible hacks and the problem still remains.

Specs:
Macbook Pro 15"
OS: Windows XP Media Center Edition 2005 via Bootcamp
Graphics Card: ATi Mobility Radeon x1600
EP Installed: EP1-EP4

backup your entire My Docs/EA Games/Sims2 folder then go through all the steps in this faq: http://www.modthesims2.com/article.php?t=139718 Please let us know how it goes.

I like found out the curpet of the freezing, it was caused by the download folder (and I had to remove more EP4 incompatible hacks..

Good to hear you found the problem files. My suggestion for the future is to put all of your hacks/mods including hacked objects into a separate, clearly marked folder within your Downloads folder. When a new EP/SP comes out you can remove that folder until you know that everything has been either updated or tested as being compatible with the new EP/SP.