I worked for company A since 2004 on H1b visa and in Nov 2005 I
transferred to A?s subsidiary in UK for an assignment. My payroll was
transferred to A?s UK subsidiary too, so my recent 6 pay stubs all in
UK. I got offer from Company B and wonder if I can transfer my H1b to
B. I confirmed with corporate lawyer that A has never cancelled my
H1b. But my H1b visa has expired. So my questions are:

1. Can I transfer H1b to Company B while in UK? If not, can I do it
while I am back into US?
2. Can I stamp my H1b visa for company A in US consulate in UK? What
documents I will need? I don?t have recent US pay stubs but have UK
pay stubs.
3. Can I enter US if I get my H1b visa for company A? What risks do I
have? Any way to mitigate the risks?
4. After I enter US, can I transfer my H1b from company A to company B
even if I have only UK pay stubs? What other documents I need?
5. What do you think is a better solution, transfer H1b or apply for a
new one for company B?

Thanks a lot!

Willworkfree,
(nice user name, but not one applicable to G-A Researchers ;)

You have asked several questions for the minimum $2 price.  If you add
a zero to the price, you are much more likely to get a useful answer. 
There are Researchers who are very familiar with US visa matters and
who may be able to help you.
You might read the FAQs.

This is a free comment.  
Good luck, Myoarin

You might want to take a look at this H1 Visa FAQ:
http://www.immihelp.com/visas/h1b/faq.html