Try downloading the Vista driver. Make sure that you select the 32- or 64-bit version, as needed, from http://support.lexmark.com/index?locale=EN&page=product&userlocale=EN_US&productCode=LEXMARK_Z605&focusedTab=DOWNLOADS#4
. Click on filter to get the correct file. To check the version of Windows that you have, click Start > Control Panel > System and Security > System. If you see x64 after the OS version name, get the 64-bit driver. Otherwise you need the 32-bit driver.
Make sure to disconnect the data cable between the computer and the printer, if you have connected it. Uninstall any problem driver (generic from the Windows OS or a failed Lexmark driver install) before installing the new driver.
If you still have problems, uninstall the driver again. Then use the compatibility mode. Right click on the exe file that you downloaded from Lexmark and choose Properties. Under the Compatibility tab, check the box for "Run this program in the compatibility mode" and select Vista. Then right click again and choose "Run as Administrator".
I hope this helps.