It's OK to print from your SD card provided that:
1. Your printer is working perfectly
2. You don't want to do anything like pre-heating your extruder, or extruding a few mm of filament to make sure everything is OK.
3. You don't want to preview a print, ot follow what is happening as it is printing.

That's why people load a program like Pronterface to make monitoring your printer easier. Read this: http://www.plasticscribbler.com/tuto...e#.VKUUXSuUdyU

You don't need high processor speed, or tonnes of RAM. You should be able to pick up a suitable 2nd hand computer from a Charity shop.

Old Man Emu