Skype spells out the following system requirements:

Windows

• PC running Windows 2000, XP or Vista. (Windows 2000 users require DirectX 9.0 for video calls)
• Internet connection (broadband is best, GPRS is not supported for voice calls, and results may vary on a satellite connection)
• Speakers and microphone – built-in or separate.
• For voice and video calls we recommend a computer with at least a 1GHz processor, 256 MB RAM and of course a webcam.
• For High Quality Video calls you will need a high quality video webcam and software, a dual-core processor computer and a fast broadband connection (384 kbps)

MAC

• Mac computer with G4, G5 or Intel processor, 800 MHz or faster with 512 MB RAM.
• Mac OS X v10.3.9 (Panther) or newer.
• For higher-resolution video a faster processor (Core 2 Duo) and a broadband connection with at least 384kbps upload speeds.
• 100 MB free disk space on your hard drive.
• Either a built-in or external microphone is required for voice calls.
• Either USB or regular headset if your Mac does not have a built-in microphone.
• Download drivers if you are using an external webcam.
• Internet connection – broadband is best (GPRS is not supported for voice calls).

Linus

• 1 Ghz processor or faster with 256 MB RAM
• 20 MB free disk space on your hard drive
• Microphone and speakers or headset
• Internet connection (broadband is best, GPRS is not supported for voice calls, and results may vary on a satellite connection).
• Video card driver with Xv support
• Qt 4.2.1+
• D-Bus 1.0.0
• libasound2 1.0.12