The valley is about a 2 hour drive north of Kabul. Turn right at Jebal Saraj and head to Gulbahar, then turn left, and left again before the bridge crossing in to Kapisa province. The road is tarred all the way from Kabul except for some rough bits passing through the towns.
There is a police checkpoint soon after you enter the valley. Have your passports ready and you may have to sign a book / give car details etc. When leaving the valley it is unlikely you'll be stopped.