First of all - why 100iu's every day??? Either do 250 iu's twice a week or 500 iu's once a week - thats all you need bro.
To answer your question - you need to obtin some bacteriostatic water - thats special sterile water to put the powder into a soulution, easily obtained. NOTE - Discard the single vial you get with the HCG - thats used to shoot the whole 5000iu's at once.
Once you have the bact water - get a sterile vial, then using a normal quage needle+barrel add 1ml bact water to the hcg powder to dissolve, then transfer solution into sterile vial. Add another 4 ml bact water to the sterile vial.
So in the vial you will have 5000iu's of HCG dissolved in 5ml of water. Therefore, if u wanna inject 250 IU's of HCG thats would be 0.25 ml of solution. 500iu of HCG would be 0.5ml of water.