US IRS Again

I got a rather threatening sounding letter today from the IRS regarding my 2008 tax return. But they did invite me to phone them to discuss the issue, which I just did. The problem was as I suspected that investment stuff was reported to them, probably by Interactive Brokers as if I was a US resident and without tax being deducted at source, yet I didn't file a tax return. The IRS will now send me a copy of what was reported to them so that I can prepare a 1040NR form for 2008 by December 15th. It's possible/probable that I don't actually owe any tax. The woman I spoke with told me that the amount I owe for 2009 is too small to file a tax return, but that they think I owe $2,000 for 2008. I have now changed my residence status with Interactive Brokers to record me as resident in Australia and this problem should be solved.