For its part, Dell, like other OEMs, has posted information on its Web site to mollify users, including details on the delivery fine print. "Dell's goal is to make the upgrade package available four to eight weeks after the Windows Vista general availability launch date," reads a Dell FAQ on Express Upgrade.

"Dell expects to begin shipping the upgrade in the latter part of February," reiterated Lionel Menchaca, Dell's digital media Manager, in a blog entry written two weeks ago.

Dell isn't the only vendor fending off angry customers. "During the past few weeks, HP has received e-mails and phone calls from customers concerning the ordering process for the Express Upgrade kit for Windows Vista. We apologize for any inconvenience that our customers have experienced," Hewlett-Packard writes on its Web site. For its part, HP said it would start shipping Vista upgrades within four to six weeks of Vista's Jan. 30 debut.

Vendors blame drivers for much of the delay. Along with Microsoft's operating system, the upgrades are also to include Vista-compatible drivers for the customer's PC and/or on-disc instructions on how to upgrade from Windows XP. "We're still validating some drivers for high-end graphics cards," said Menchaca of Dell.

Neither Dell nor HP officials were able to immediately say whether the Vista upgrades are shipping, and if not, when the first kits would go out the door.