Hi guyz, i agree with ganesan, and u have to do the internal audit depending upon the scope given by the management and agreed by the auditors.
As far as the format of the reports are concerned, there is no such format infact every firm (CA firm) has its own format of presenting the report and also in few cases the client itself will specify a particular format.
1st place you should look for a format is in your own office and if u dont have one, then use the simple MSword giving separate points and paragraphs such as: Scope, Background, Observations, Risk and implication and the recommendation and also the auditees reply.
..(sorry to disappoint but u have to make ur own format)