I've looked through the forum and wiki, but I can't find the answer to my very simple questions; What are import files and can I delete them? What are tmp files? That's all I want to know and I can't find the answer anywhere.

These files are part of the process of installing lots - they should vanish when you run your game. Where have you found them?

in my downloads folder

Hmm that's odd, they should be in Teleport, not Downloads. I don't know how the naming works, so it may or may not be obvious which lot they correspond to. Have you used the Q-Xpress to install stuff at any point? If someone had zipped up the wrong files for a lot this could explain it, although it's still strange.

Either way, they're not doing you any good in Downloads, you may as well delete them. I know from PM you're experiencing game crashes - are you sure it's custom content related? If so, have a look at this FAQ, if you haven't already: Game Help:Finding Problem Custom Content^wiki. And if not, use this one: Game Help:Game Problem^wiki.

actually it's import files, not teleport, but I'm going to try and delete them anyway and see what happens

If you are using the clean installer, it is possible to change the install location to the Downloads folder with the 'generate Sims2Import file' ticked. That will fill your Downloads folder with temp and import files, with which the game will do nothing. Is it possible that you have installed a lot or sim in this way?

i think i have done that. So is it all right to delete them?

Yes- you'll probably want to install that sim again, though. If you use the Clean Installer, remember that the import files must be installed to the Teleport folder. The content alone can be installed as package files directly to the Downloads folder.

Okay thanks. What about the TMP files? Can those go too?

Yup, they can.