The minimum system to run Machinekit and Debian may vary depending on the exact usage.
Stepper systems in general require faster threads to generate step pulses than servo systems. Keep in mind that the Latency Test numbers are more important than the processor speed for software step generation.
More information on the Latency Test is Here
Machinekit and Debian should run reasonably well on a computer with the following minimum hardware specification. These numbers are not the absolute minimum but will give reasonable performance for most stepper systems.
1.2 GHz x86 processor
1GB RAM minimum recommended
8 GB hard disk space minimum
Graphics card capable of at least 1024x768 resolution, which is not using the NVidia or ATI fglrx proprietary drivers, and which is not an onboard video chipset that shares main memory with the CPU
A network or Internet connection (not strictly needed, but very useful for updates and for communicating with the Machinekit community)
Laptops are not generally suited to real time software step generation. Again a Latency Test run for an extended time will give you the info you need to determine suitability.
If your installation pops up with 800 x 600 screen resolution then most likely Debian does not recognize your video card or monitor. Onboard video many times causes bad real time performance.