I really want to go to graduate school (full time). 

I am currently working as a Software Engineer with an H1B status for
my second company. The second company requested a 3 years period of
H1B visa.

I worked for about 2 years with my first company and transfered my H1B
to second company. It's been 6 months now since I joined my second
company, and would like to quit working to become a full time students
(to change status from H1B to F1).

What happen to my H1B if I switch to F1? If I found a company to
sponsor me after completing my graduate school, will I still have the
remaining 3.5 yrs (6 yrs - 2 yrs of my first job - 1/2 yrs of my
second job = 3.5)  ?

Please include proof of evident (goverment website) of your
information because my legal status lies on your information. Greatly
appreciate!

Noodle Studio,
  You don't lose your H1 B years even you go to the school now.

Following link will give you more on this information.

http://www.h1bsponsors.com/html/h1bExtension.html

This is true and you can clarify with your lawyer.


http://www.hammondlawfirm.com/monthly/bus_imm_monthlyNov05.htm
..following give more information on this.

Hope this helps.

Noodle Studio,
May I point out that the links given by Dream279 are to commercial
sites and not the US government's US Citizenship and Immigration
Service.

http://uscis.gov/graphics/howdoi/h1b.htm
On the above page it says that employment must be continued to
maintain H-1B status.
On this following page, however, you can click for information about
changing your nonimmigrant status to that of student:
http://uscis.gov/graphics/howdoi/academic.htm

You can click on FAQs at the top to access more information.

The www.h1bsponsors site mentions changing status, but FROM F1 to
H-1B, not the other way around.  I must have overseen any applicable
information on the other site.

OF COURSE, none of this is professional or legal advice, as you can
read in the disclaimer below.
I wish you good luck, Myoarin