It's no secret that the past few years have been the era of the frozen IT budget. As the global economy went south in 2008, most enterprises went into belt-tightening mode. Now a thaw is beginning, according to a new report by research firm Forrester, as tech spending is set to increase and major corporate PC refreshes are scheduled for the next 12 to 18 months that will introduce a new operating system, productivity suite, browser and applications. While this is great news for Windows 7, it opens up a new set of challenges for the Internet Explorer browser.Forrester anticipates that IT managers will begin major corporate PC refresh cycles by mid-to-late 2010. Enterprise-wide adoption of Windows 7 will likely occur at the same time, according to Forrester, as IT managers develop upgrade strategies, test their applications, and figure out if client virtualization is part of their plans.The Forrester report emphasizes Windows 7's quick pace of adoption. Released on Oct. 22, 2009, Windows 7 is already powering 7.4 percent of corporate PCs, according to Forrester's analysis of 90,000 PCs across 2,500 different worldwide companies, which is a level Windows Vista did not reach until almost a year after its release.From Q2 2009 to Q2 2010, Windows 7 usage by 81,000 Forrester enterprise clients jumped from 0 percent to 7.4 percent, while in the same period Windows XP usage dropped by 7 percent to 74.8 percent. Vista usage remained flat at 12.6 percent.[ For complete coverage on Microsoft's new Windows 7 operating system -- including hands-on reviews, video tutorials and advice on enterprise rollouts -- see CIO.com's Windows 7 Bible. ]Yet despite rapid enterprise adoption of Windows 7, the Forrester study points out that the consumerization of IT and companies instilling BYOC (bring-your-own computer) programs has generated more interest in Macs within Windows environments. This is typically done through desktop virtualization tools such as Apple's Boot Camp, VMware Fusion and Parallels.Mac OS usage among Forrester enterprise clients grew slightly over the past year, from 3.7 percent to 4.0 percent.Internet Explorer: Feeling the HeatWith corporate browser usage, Microsoft faces a much bumpier road. Although Microsoft's Internet Explorer is still the leading browser at enterprises with 72.5 percent usage, it had a year-over-year drop of almost 5 percent according to Forrester's data. Mostly this is attributed to businesses that replaced Windows XP systems that had IE6 as the default browser and then chose to use Firefox or Chrome instead of IE8.While IE's overall usage dropped among Forrester's clients, usage for Firefox increased by 3 percent to 20 percent of overall usage, and Chrome increased by 4.6 percent to 6.9 percent of overall usage. Safari usage declined by a full percentage point to 0.44 percent.\nSlideshow: Seven Features in Windows 7 You Probably Don't Know About\nSlideshow: Windows 7 in Pictures: The Coolest New Hardware\nSlideshow: Seven Tools to Ease Your Windows 7 Rollout\n\nForrester states that Firefox has gained ground because, "unlike with IE, Firefox users have quickly embraced new releases, with 17.6 percent of the market using Firefox 3.5, 2.1 percent using Firefox 3.0, and less than 1 percent still on Firefox 2.0."Regarding Chrome, Forrester anticipates that the browser will continue its slow climb in the enterprise as devices like netbooks flourish and European consumers are made aware of IE alternatives because of Microsoft's settlement with the European Commission.Forrester advises that IT managers upgrading to Windows 7 make sure that Web applications are compatible with IE8, given that it is the required version of the new operating system. The research firm also recommends that businesses upgrading to Windows 7 invest in application virtualization to ensure that legacy applications such as IE6 and older versions of Office still work without conflicting with other applications.Shane O'Neill is a senior writer at CIO.com. Follow him on Twitter at twitter.com\/smoneill. Follow everything from CIO.com on Twitter at twitter.com\/CIOonline.