I got strange behavior of selected text (see attached image) on my old Dell laptop (P3, ATI Rage Mobility 128 AGP2X, 32 bit color, WinXP SP2). The selection is rendered fine on newer computer with NVidia Geforce4 video card.
Can you run Sublime Text with --opengl on the command line (requires 20080327 or newer), and let me know if it still happens?
With --opengl command switch selections are rendered correctly on both Geforce4 and Ati rage mobility 128.
The next beta will require slightly next of the D3D driver, so it may work without OpenGL, but I'd assume not.