1/2 marathon training needs

[KMK]

I tried 3 weeks ago to run the 5 x 2000m, but I gave in after 6.58 and 7.02, since I was afraid to injuring my hamstrings, that had been quite tense up to that day and became tense during the 3rd interval. Otherwise I followed the program, with the 6 x 1000m @ on avg. 3.22 and the 5K @ 17.42 on a sandy path. I should have run the 5 x 2000m yesterday, but had a slight cold, and thus ran today instead on a track @ 6.57, 6.57, 7.02, 7.04 and 7.05. So the speed is not quite there yet, but I felt ok during and after the run.
What speed do you recommend for the 2Hrs longest run, when I am preparing for the ½-marathon in 5 weeks time? Is any hill work recommendable?
Br. Karsten