APK downloads are the Android Apps. If you don't "trust" those then you are going to have real problems with getting apps on your device. If what you mean is you are concerned about virus infection or other threats, there is an app called Lookout that will scan any APK or other file that is downloaded to make sure it is safe for you to use.
As far as finding the link, the search function is your friend.
As of right now AFAIK there is no way to get Android Market to function on the Creative tablets. This is because the Android Market is only made available to devices that have been "certified" by Android, which hasn't happened yet. What usually happens on tablets like yours is that some developer out there gets one and then figures out how to extract a working market from another ROM, and make it work on a Creative. Part of the issue is in the hardware requirements for Android Market, which your tablet does not meet (having phone capability). Until they change the rules, that is going to continue to be the challenge.
In the interim, you have to use other methods to get apps. I know that Creative has their own market specifically for their tablets with apps that they know work, otherwise there are options such as AppBrain or other sideloading services.