I had it crash to desktop straight after loading (about 20 seconds of actual ingame before the crash) and having had a similar problem on Fallout 3 that a modder on a forum had fixed, I decided to give it a go with this. It worked for me, maybe it will for you:
Download and install (I am not a bot or an evil virus-spreader, honest folks!):
Go to "C:\Program files\Electronic Arts\The Sims 3 Ambitions\Game\Bin"
And find a program called "TS3EP02"
**Copy this file somewhere where you can find it again, we need to make a backup (for when EA releases an official patch)**
Right click the original file > "open with CFF explorer"
You now have a window open "CFF explorer - [TS3EEP02]
On the left, under "NT Headers", there should be a tab called "File Header" Click it.
Then click on the area, towards the right of the window, labelled "Click Here"
A "Chacteristics" box will open. Check the option "App can handle >2gb Address space"
**MAKE SURE YOU HAVE DONE THE BACKUP AS I SAID EARLIER**
Close CFF explorer
save changes to original file.
Hopefully it will work for you too. :)
When EA releases a patch that fixes this, or if this didn't work for you, simply find the original copy you made (because you did do that didn't you?) and overwrite the modified file with the original copy. This will allow the patch to install (because it won't on a modified .exe) and will revert the changes we made above