iPod mini just came into stores this weekend. there have been over 100'000 pre-orders, but other than that, numbers are, of course, not yet available. much too early to compare iPod to iPod mini sales...
however, in order to convince your buddy to buy an iPod, there are a few simple steps you should do...
1.) let him _use_ one. touch one. when you get your iPod mini, go to him and install it on HIS machine to show him how well it works. he'll love iTunes, anyway!
2.) get some numbers by searching the 'net for 'ipod market share' and 'itunes market share'. there have been a lot of articles about it around the web lately.
3.) do NOT try to tell him that dell is bad. it's a) not worth it and does b) not help if he likes dell. imagine someone telling you how bad apple is and what your reaction would be. sure, it's not the same, but the basic patterns still apply.
4.) do question him about what's most important to him in a digital music player. the iPod is king in most areas, anyway. also make sure that he gets the fact that the iPod, while a bit more expensive, also GIVES a lot more. more luxury, more ease-of-use, more durability (there's some thread to be found on macosx.com about someone who let his iPod drop out of a running car accidentally - the iPod survived...).
5.) make sure he gets the fact that apple improves the software of the iPods on an almost regular basis. you don't have to tell him that first generation iPods aren't able to use much of the later enhancements, but you can tell how apple has added support for iSync and stuff and that you can use the iPod as your address book, newsreader etc. if you want to. not that most people really _use_ it that way. then come back to its basic functionality, which just rocks. show him again and again, how easy it is to synch, that it always works etc. pc people tend to know bad things about synching. (well, so do palm users, but hey...) ;-)