In summary.... however here are the most common resolutions. This turned into a slight rant... so umm... sorry!
 
Reinstall the game!
Goto Windows Update and install all of the updates
Get the lastest drivers for yor graphics card
Get the latest chipset drivers for your motherboard
Download DirextX 9.0c
Download something like CCleaner and clean your PC
Defrag your hard disk(s)
Go here and use the utility to defrag.
Go here and read the thread and use all of the tools that you feel comfortable with. APK is always around, so any questions just post.
Be very careful using any kind of "NOCD Crack". Only try if the game still doesnt work (useful for older CDROM drives though).
Disable any uneeded Services. Go here and follow the Services guide.
Flash your BIOS to the lastest version (be careful)
To get help from EA go here.
 
 
OK so thats the kinda 'general' housekeeping done.
 
Now, the rest.
 
Dont moan if your graphics card is old. S3 and 3DFX are DEAD. They maybe in Video Heaven however no amount of praying will work!!! Something like a nVIDIA GeForce2 or better should suffice. Handy list of cards here.
If you have Integrated Graphics the chances are that they are not beefy enough to run the game. If you have a non-T&L capable video card, such as Intel Extreme Graphics or Radeon VE series, then you need at least a 2.0 GHz processor.
Have enough RAM and make sure it is fast! It doesnt matter if you have 1Gb of slow RAM... you would be better off with 512Mb of fast RAM! Read up on DDR and what it means.
DO run the checking utilities provided for the Sims 2. Get them here.
 
Accept the fact that you may just have to change the graphics levels to LOW or even OFF
 
Goto Google and type "tweak <your graphics card> guide". Tweak away.
 
Read up and learn about the following:
Corsair, OCZ, Crucial, DDR, Mhz, AGP, PCI-X, SATA, DirectX, DXDIAG, ID, UDMA, chipset, PSU, ATI, nVidia.
 
Erase the following from your brain:
PC100, S3, Windows 95, Single Speed, TNT
 
Uninstall ANY software that meddles with refresh rates. Programs that FORCE refresh rates make Sims 2 go bonkers.
 
try reinstalling DirectX 9. To do this:
> Open My Computer.
> Right click on the Sims2 icon and choose Open
> Double-click on the DirectX folder.
> Right-click on the DSETUP.dll file and choose Copy.
> Close this window.
> Open My Computer again.
> This time, open your C: drive.
> Now open the WINDOWS folder.
> Open the SYSTEM32 folder.
> Right-click on an empty space in the folder and choose Paste.
> Now try running the DirectX installation again.
 
 
If all else fails, post a question.... or upgrade! Sims 2 pushes the boundaries just that bit more, which maybe more than your PC can handle.