Is margin allowed in IRAs?

I thought that using margin in an IRA would be considered “pledging the account as collateral”, thus making it a prohibited transaction, but I’ve come across a few articles (see excerpt below from http://www.myaffiliateprogram.com/ target=”_blank”>Traders Accounting for one example) that seem to view the topic differently.

[i]IRA Margin Trading

The IRS has specific guidelines for trading your IRA on margin called the debt financed income rules that essentially ensure the government gets a cut of the profit. Still, by IRS standards the split is a generous one: you only pay tax at the corporate tax rate on the profits you make on the borrowed money alone.

Here’s how it works: Say you use your $80,000 IRA to purchase a position for $100,000. When your IRA exits the position with a profit of $50,000, 20% of your profit, or $10,000, would be subject to tax because you borrowed 20% of the IRA amount ($20,000) to make the margin trade.

IRA Short Sales

Hard though it may be to believe, the IRS doesn’t view borrowing stock against your IRA and selling it within your margin account as incurring debt (IRC Revised Rules 95-8). That means you get to keep every penny you earn on a short sale, tax-free within your IRA, without facing the debt financed income rules. [/i]

In doing a little more research, there seems to be a lot of conflicting information on the topic. Can you shed any light on the issue?