im converting my front speakers to 6 1/2's and i want to get tweeters, im just wondering what crossovers do and if it is worth getting them.. thanks

Just get a set of components....they will have the 6.5's some tweeters and the crossovers. The crossovers just allow certain frequencies to go to each speaker. It will allow mid tones to go to the speaker and high pitch noises to go to the tweeters. Improves the sound alot and eliminates bass coming through your speakers. Alpine makes some nice components IMO.