The major changes to Windows XP brought by Service Pack 2 -- due this quarter -- are bound to cause support headaches. Analysts, users, PC makers and Microsoft Corp. all expect a spike in help desk calls. The service pack automatically will be downloaded into many PCs through Microsoft's Windows Update service and could create problems, including breaking current applications, disrupting network setups and prompting nontechnical users to make PC configuration decisions that might be beyond their grasp. Microsoft will offer free, worldwide telephone support for the service pack. Microsoft is returning to its policy to provide free support for service packs after leaving support for Windows XP SP1 to the PC makers. Nevertheless, Hewlett-Packard Co., Dell Inc. and Gateway Inc. also are gearing up for the release of SP2 and will support their customers, spokespeople for the PC makers say.