India
India's key is their batting, but as was seen in the practice game against Pakistan A, their bowlers might struggle this time around. A lot depends on Harbhajan Singh and Anil Kumble, but I dont think the wickets will help the spinners as much as in India.
India's two key players are Rahul Dravid and Sachin Tendulkar. I think for any opposition, if you manage to get these two out, then you can safely say that you've done 40% of the job. However there are other players who on their day can cause problems as well. Virender Sehwag, though highly unpredictable is capable of scoring big knocks. The likes of Yuvraj Singh, Gautam Gambhir and Wasim Jaffer have talent, but dont pose as much of a threat as the previous three players I mentioned before.
The dark horse in the Indian batting lineup is Saurav Ganguly. He however needs to first find a place in the starting lineup. This could be a make or break series for him, and I for one believe he can play a crucial and decisive role if given the oppurtunity. He does need a bit of luck also.
Mahendra Dhoni will hit his sixes, but thats pretty much it. Irfan Pathan might get another surprise 50 or 100 in one of the innings, and improve his tag of an allrounder even more.
But the bowling is a worry. Irfan Pathan is being hailed as India's newest allrounder, and has done a good job so far. But I think over the past few years while his batting has picked up tremendously, his bowling has been disappointing. He has been very inconsistent with the ball, and very rarely does he perform well with both ball and bat in the same match. I havent seen much of India's newcomers RP Singh, etc. and I do not rate Ajit Agarkar very highly as a bowler, though on his day he can bag 4-5 wickets. Unfortunately one good match is followed by 3-4 bad ones.
The bowling hence depends purely on the spinners, Harbhajan and Kumble. But if you check out on the last series in Pakistan, I think it was one certain Shoaib Akhtar who was the highest wicket-taker. And despite the fact that England's batsmen struggle against spin, I thought they had a really rough time facing Akhtar and Naved.
Hence I dont think the wickets will suit the spinners as much as they do in India.
Pakistan
Pakistan too have a strong batting lineup with the likes of Salman Butt, Younis Khan, Mohd. Yousuf and Inzamam all in very good form after the series against England. I would pick Mohd. Yousuf, Salman Butt and Inzamam as the three key batsmen for the home side. Kamran Akmal is the dark horse, and believe me this lad can score runs!
Pakistan have the clear edge in bowling. Shoaib Akhtar is in the form of his life, and bowled brilliantly against England. Watch out for him. Mohammad Sami has been fairly silent, but he too is a fine performer. For India's sake I hope he remains silent in this series as well. Danish Kaneria, Shahid Afridi and Shoaib Malik represent Pakistan's spin department, but I dont think they'll trouble the Indian batsmen much as the latter are the best players of spin bowling in the world.
In Abdul Razzaq they have an excellent allrounder, and I consider him as another key player in the Pakistan side, and one who could make the difference. Definately the best genuine allrounder from both sides combined.
Key Players for India:
Tendulkar
Dravid
Kumble
Harbhajan
Key Players for Pakistan
Inzamam
Mohd. Yousuf
Salman Butt
Shoaib Akhtar
Abdul Razzaq
My Predicition for the test series:
2-1 or 2-0 win for Pakistan (assuming bad light does not stop play)