My wife has valid H1 till dec 2010. But the problem is she does not have a job now. My questions are
1.can we still apply for change of status what are the documents needed?
2.I am a H1 holder.does change of status requires any pay-stubs or W2 of my wife or mine?
3. Can we travel outside US after getting change of status/ do we need stamping for h4 again?
4. What if I want my wife wants to get H1 again?
5. Will the previous H1 of my wife is void and have to apply for new H1?

If she is in status and qualifies for the H-4, she can apply for the COS. You need to show you are currently in valid H-1B status and that you are married.

You need to be in current H-1B status for her H-4 COS. The USCIC may issue and RFE for evidence of your current H-1B status.

She will need the H-4 visa stamped in her passport to enter the US as an H-4. her current H-1B visa doesn't allow her to enter as an H-4.

If she has another H-1B petitioner, they file the COS, same as her previous H. she will already have been counted for the H-1B allocation so she can file at anytime (if she hasn't used up all 6 years for H-1 eligibility).

H petitions are employer specific. She needs a new H petition and I-797 approval notice.