The discounted upgrades were offered starting last October to buyers of Windows XP-equipped systems, and were a amid complaints from computer makers that they would miss out on holiday hardware sales.

Users expecting a fast turn-around of Vista DVDs, however, have been disappointed.

"I drop over $3,000 on an XPS 710 and have to wait longer for my upgrade? Waiting until the end of February to receive an OS that I could walk down the block and get a week ago is crazy enough...now I call and I'm told the earliest is late March for this to ship," wrote a user identified as "Jason" on an official Dell blog.

Another, who gave the name "Scott," said: "Why is it that an 'express' upgrade won't even be shipped until almost a month after the release of vista[?] I feel like a chump, thanks for all the delay and poor excuses. I wish I would of [sic] bought an apple."

"I could have waited until now and bought a brand new machine with Vista pre-installed, but instead I have to wait until the end of February or beginning of March for an upgrade," complained "Phil."