Not really, DMC2 wasn't fantastic and didn't really add huge amounts to the general plot, and while DMC1 was great, it isn't really necessary to understand the actual plot behind the series, really and truly the only thing you'd really be missing out on is how it all started with DMC1, aside from that, I wouldn't be too concerned if you can't get a hold of the previous 2 installments.
3 is a brilliant game in itself, as is 4, frankly I think the storylines of each Devil May Cry game to date have been pretty standalone, it's not really like you actually HAVE to have played the previous games to get your maximum enjoyment out of 3 and 4's storyline.