ok so whenever i try to open steam or undead, it says it cant find steam.ddl, which i do have. I tried to reinstall, but that did nothing, because when i press run, it says that its not a valid windows installer package
Uninstall it, restart your computer, then delete the whole steam directory. If you have either profiles or GCF files that you've downloaded/made, back them up too. Reinstall steam, then try the undead patch. If that doesn't work, try installing steam to a different directory and see if that's any better.
If you want to try and uninstall it properly, try a program called "Your uninstaller" and also download a program called Crap Cleaner. Try using both of them to uninstall it. If that fails, then do safe mode. Just go Run -> msconfig -> boot.ini then tick "/safeboot" and restart. Then when you're done, untick "/safeboot" and restart again