out dated UDK specs
Minimum PC Requirements for Users
Windows XP SP3 (32-bit only)
2.0+ GHz processor
2 GB system RAM
A graphics card with shader model 3.0 support.
Minimum PC Hardware Requirements for Developers
Windows XP SP3 (32-bit only) with DirectX 9.0c
2GHz or better CPU
2+ GB RAM
A graphics card with Shader Model 3.0 support, such as nVidia GeForce 7800
NOTE: Windows 7 64bit is currently the mainstream development environment.
Recommended PC Hardware Specs for Developers
Windows 7 64-bit
2.0+ GHz multi-core processor
8 GB System RAM
NVIDIA 8000 series or higher graphics card
Plenty of HDD space
i would say any thing higher then to the recommended dev specs ... best bet is do your research on "gaming laptops" there are some good ones out there now but a desktop will always be cheaper
any multicore 3.0Ghz cpu, 8gb+ ddr3+ ram, GPU bigger the better