I think this should work for mini's too and may sound a bit odd, but bear with me here! There are various methods....
First download the Handcent Sms app and once you have it go back to your Menu>Settings>Sound & Display>Phone Ringtone (the sequence may be slightly different on a mini but you get the gist) now when you tap on Phone Ringtone it gives you two choices... Android System and a blue speech bubble that says Select Music and you can then view all your music on the phone and select one as a ring tone... assuming thats where your ringtone has downloaded to.
The other method I have only read about but you could give it a go, is to download a file manager Astro for example and then copy the downloaded ringtones from wherever they are saved and paste/move them into a 'ringtones' folder and apparently the phone can then 'see' them in that.
Third option, is the app called Tone Picker, again only heard about this one not tried it.
Let us know how you get on with it!
