iWork not installing, please help!

Okay, just got a mac mini and accidentally delete all the iwork trial stuff off of it, now when I try to install iwork disc purchased it's not allowing me to saying that I have an updated version on my harddrive and shows my harddrive picture with a stop sign saying "you cannot install iwork on this volume. A newer version of this software already exists on this volume." Although mac's support site says to just enter the code on the trial version after pressing buy. Although I no longer have the trial version, yet it says I still do when i try to install the disc. What do I do if I can't open the trial version, nor can I install it from the disc due to this restriction, please help! Thank you in advance too

 

Thanks for the help, I figured it out! I had to delete the trial receipts of iwork from my library/receipts folder. So many new things to learn being a new Mac User, although soon I may have to claim being a full-fledged switcher, not only are the computers helpful but so is the mac community - thank you for the help! Problem solved, iWork '05 loaded