Dinsey, if your wife has a two-year spouse visa then are you sure it expires in July 2007? Why do I ask? Because we are not yet in July 2005. Did she ask for the start date on the visa to be delayed?
When to apply for ILR? In the last 28 days of validity of the existing two-year spouse visa. So sometime in June or July 2007 (if the current visa does indeed expire in July 2007).
To apply for the ILR then your wife will use form SET(M) which can be downloaded by
clicking here. Even though lots of time before you will apply it is still worth downloading the form now if only because Note 2 of page 15 of 19 of the PDF file details the sort of information that IND will require, in order to prove that the two of you are living together in a proper marriage (rather than it being a marriage of convenience).
Note that evidence is required from the first of the two years, and also from the second of the two years, so worth starting to give some thought to building up your evidence.
Do appreciate that the form and the fee for applying is highly likely to change in the next two years. So the current form should only be considered a guide for you.
The holiday in India? That will make no difference to when the ILR visa should be applied for. Presumably your wife will not be having an extended time in India? I ask that because when she applies for ILR it needs to be clear that she is indeed settled in the UK (rather than using her spouse visa like a glorified visitor's visa).
How long before she can apply for a national insurance number ie work in the uk?
If she has a spouse visa then she can work in the UK. She should contact her local Job Centre, but don't be surprised if they say she cannot make an appointment for a NINO interview before she actually has a job. The spouse visa in her passport confirms she is able to work and she should expect to need to show her passport with its visa to any prospective employer.