Microsoft certainly has a lot of catching up to do with Windows Phone 7 — its upcoming mobile platform. In particular, it’ll be interesting to see how its Internet Explorer 7 mobile browser will compare to Apple’s Mobile Safari and Android’s browser, both of which are based on the fast Webkit browser framework.

Thanks to mobile site PocketNow, we have the closest look at Windows Phone 7’s web browser yet, in the form of a lengthy video comparison to its competitors (see below).

The site put an early Windows 7 device (the LG Panther) head-to-head with an iPhone 4 and Nexus One, and the results were surprising. The tester attempted to replicate simple web browsing tasks like searching on Google, dealing with tabs, and visiting complex sites. Microsoft’s IE 7 mobile browser managed to hold its own with fast web browsing speeds, a zippy interface, and arguably better tab management than the competition. Overall, it’s an impressive effort from Microsoft, and a clear sign that it’s taking Windows Phone 7 seriously (unlike its doomed Kin phones).

By the time finalized Windows Phone 7 hardware is released some time this fall, the browser will likely perform even better than we see here. That’s particularly important for Microsoft, since mobile web applications depend entirely on the speed of the browser, and other applications will depend on it for in-app web browsing.