The Epic Games Forums offer a translation of information found in PC Games Hardware, a German gaming magazine, where Epic's Tim Sweeney sheds some light on hardware and software support for Unreal Tournament 3 (thanks BeyondUnreal). Here's a bit:

PCGH: Will SLI and Crossfire provide significant advantages?
Epic: We're testing SLI configurations on a regular basis. Their positive influence can be felt significantly, especially at higher resolutions. So, if one wants to have full details at very high resolutions, a SLI-system would be the ideal way to secure optimal performance. We had no opportunity to test crossfire systems yet, but we are expecting similar results.

PCGH: How exacly are you utilizing the functions of Direct X 10?
Epic: Unreal Tournament 3 will ship with full DX10 support, with multi-sampling being the biggest visible benefit of the new graphics interface. Additionally, with DX10 under Vista we have the possibility to use the video memory more efficently, to be able to display textures with a higher grade of detail as it would be possible with the DX9 path of Vista. Most effects of UT3 are more bound to the fillrate than to basic features like geometry processing. That's why DX10 has a great impact on performance, while we mostly forgo the integration of new features.

PCGH: Will UT3 players be able to benefit from a 64 Bit environment and is there a 64 Bit version anyway?
Epic: To assure compatibility, we tested UT3 with Vista x64 as well. Nonetheless, we're planning to wait and see first, until the OS and its applications will have ripened, before we'll be taking further steps in the 64 Bit direction. With UT2004 we were one of the first developers who ported a title for Windows XP x64. We would've liked to do this with UT3 and Vista x64 as well as shifting all the PCs we're currently developing on to the 64 Bit version of Vista. Unfortunately, full software and driver compatibility isn't there. The basic OS runs stable and it's fun to work with it isolated. But as soon as you want to print something or want to run Maya or 3DSMax together with some third-party plugins you'll get massive problems. But I am sure those can be fixed via service packs and software updates, so PCs with 4 to 8 gigs of ram can establish themselves during the next 12 months.