Who told you that you could not Petition your wife as a Permanant resident, a lawyer or USCIS? If your lawyer, I would suggest you get a second opinion Below is a link to the process and it does indicate that..

"If you are a lawful permanent resident you may petition for the following foreign national relatives to immigrate to the United States; however you must be able to provide proof of the relationships:

Husband or wife; or
Unmarried son or daughter of any age. "

http://www.uscis.gov/graphics/servic...ncy/family.htm

One thing I would think "might" be an issue is that the "permanant residency" or green card is considered "temporary" for two years, so you may have to wait until it really becomes permanant. Or, the passage states that you can petition relative "to immigrate". There may be a specific problem if the spouse is already here..

There may also be some other circumstances that you may think are not relevant enough to mention here, that could be an issue. For instance, you indicated that you both entered legally, on VISA's, but do not have the documentation. That could be problematic in proving that you entered and may cause the petition through permanant residency more difficult.

I would suggest you study the USCIS web site, specifically the link I gave, and show the passage to the Lawyer and ask what, very specifically, is preventing you from petitioning as a permanant resident. If you still think he is not quite right, make an appointment through INFO PASS (same link, home page) and talk to the USCIS directly.

Finally, to answer you last question, There is no guarantee...no matter which petition process (Citizen, perm Resident, ) you still have to follow all the same processes and procedures.