I've been using my Sony Vaio laptop with my Samsung SyncMaster 2494HS display for a month or so now. Everything was fine via the VGA cable, 1920x1080 resolution @ 60hz.
However, I wanted to use the VGA port of my display for my Xbox360 and therefore bought a HDMI cable so that I could use the Laptop via the HDMI cable.
My graphics card is a nvidia 7600 go and ever since I plugged in the hdmi cable, i realized that I couldn't select 1920x1080 @ 60hz but merely with a 30hz refresh rate (or 29 or 25). I believe the window shaking that has appeared is due to the refresh rate, since it works fine at 1440x900 @ 60hz.
However, I'm a fan of high-res and that's the reason I bought this laptop and this display. Anybody have an idea how I can fix this issue?
Cannot fix, GF7600Go's HDMI output is a single link TMDS output, cannot handle 1920x1080x60hz, it was designed with TV output in mind supporting 24frames, 25hz PAL and 30hz (29.97 is NTSC/ATSC standard) this was an issue that was addressed in the GF8600 series.
It wasn't something people considered in the past unfortunately. ATi still is single link, but they boosted their TMDS speed to double, which allowed them to fall back to dual link via active adapter, but allowed them to support the standard 225Mhz single link speed of most video gear currently out there.
Remember this was a standard still young and in flux while these things were being designed, in this generation neither had full HDCP compliance either, only optional compliance with partial key support, simply because next no one needed it at the time, heck external HD-DVD/BR support didn't occur until late into those generations, so if it didn't ship with a BR or HD-DVD drive there wouldn't have been a need initially.
I'm not making excuses for the companies, they suck, but just saying you could've fully researched this and likely never found out about the issue, unless you read one of the handful of reviews that talked about it but were ignored and overlooked by most people.
One thing you can try is to hack in support, being a SONY they may have added support for the HDMI out via an external Silicon Image chip just because they may have standardized the support for the potential of their BR equipped models, alot of ATi and nVidia laptops that shipped with BR drives had those chips instead of the integrated HDMI/TMDS support. However this is not an easy thing to research, likely the only source will be Sony forums checking for threads/questions/faqs that have already looked into this issue.
You can try forcing it with either a regedit hack or a tool like Rivatuner, however you want to be sure that it's supported both by the graphics chips and your moitor first, because randomly applying those types of changes, damges monitors and can cause issues with some chips (although it's harder to fry a GPU/TMDS/etc).