how to hook a tweeter to a 2 way speaker

Was the tweeter part of a component setup?  If so the crossover that came with the setup is a vital part of the speaker system.  If you do not have the crossover, do not connect them they will not last.   If they were purchased as a stand alone tweeter, there should be a capacitor in series with one of the wires, if so you can connect it to the wire that you connected to the Alpine speaker. 

the tweeter  was originally in my other car, hooked to the crossover, then to a 6.5" mid (adire koda 6 i believe).  The 4" speaker that i have in my new car has a capicator on the back of it , but it has like 5 different connection points so I kinda figured it would work as a mid and use the tweeter for highs without a crossover or amp..but wasn't sure if itd sound better then just using the 4" two way or how to hook it up.

the 2-way speaker is a alpine sps-100a I believe.

You can use the following capacitor, http://www.radioshack.com/product/index.jsp?productid=2102480&cp=&sr=1&kw=non-polarized&origkw=non-polarized&parentPage=search 

in the following manner,

High Pass filters allow high frequencies above a selected crossover frequency to pass, filtering out all frequencies below it. In a first order (6dB per octave) filter, this consist of a capacitor in series with a loudspeaker. Just above the crossover frequency, the capacitor begins to add resistance to the circuit. At the crossover frequency enough resistance has been added to equal the resistance of the loudspeaker and reduce the power by 3 dB or 50 %. One octave below the crossover frequency, power has been reduced by 6 dB or 75%. Each octave lower reduces the power by an additional 6 dB. The size of the capacitor will be determined by the impedance of the loudspeaker(s) and the desired crossover point. The smaller the size or value of a capacitor (microfarads, µfd or mfd) is, not physical size, the higher the high pass frequency will be.