Converting .docx,.pptx to .doc,.ppt files online

Not sure what version of Office you are running, but the Microsoft Office Compatibility Pack may be your answer. http://www.microsoft.com/en-us/download/details.aspx?id=3 Says it works with Office 2000, XP, and Office 2003. It simply allows these older versions to open, edit, and save the new formats. I know it's not online, but you may not need to go online to solve the problem.

You might look at the http://www.microsoft.com/office/preview/en (It should have an online, web-based version of Word/Excel/Powerpoint), which should be free for the time being until it's released / the preview ends, and in the future will allow you to use MS Office applications online if you've purchased office. Due to the proprietary nature of MS document formats, I doubt you'll get accurate reproduction of them in anything other than office. For offline tools, OpenOffice and LibreOffice are your best bet, and I'd recommend downloading one or the other if you're against purchasing MS Office and need as accurate reproduction of layouts as you can get. I've not tried the Office 2013 preview yet, but I hope they have accurate reproduction of the documents online. Otherwise, I think gdocs is as good as it gets, as terrible as it is at opening MS-formatted documents.