If you are a British citizen, then your wife will be eligible in March 2011.
Those married to British citizens must meet the following requirements when they apply:
1. Aged 18 or older
2. Sound mind
3. Ability to communicate in English to an acceptable degree
4. Sufficient knowledge of life in the UK
5. Good character
6. Residence in the UK for three years as of the date of the application
I take it that your wife meets parts 1 and 2 above.
Parts 3 and 4 are demonstrated by passing the Life in the UK Test. Provided she did this to get indefinite leave to remain, she can rely on this when applying for citizenship and need not take the test again.
The good character requirement is only an issue for those who have convictions, civil judgments, or bankruptcies. However, some convictions for traffic violations or TV licence evasion can be a problem for some.
Please note that part 6 above requires that the applicant must have been physically present in the UK exactly three years before the date on which the Home Office receives the application. If your wife arrived on, say, 1 March 2008 and went on holiday outside the UK between 15 March and 20 March 2008, then she should not not apply on any anniversary of a date on which she was on holiday.
An applicant must not have been outside the UK for more than 270 days in the three year period ending with the date of the application. An applicant must not have been outside the UK for more than 90 days on the one year period ending with the date of the application.
You can get more information at
the Home Office's web site.