You've not stated which software you're using. If it's Microsoft Word, it's got a built-in ability to produce business cards. Word assumes that you're using business cards on a scored A4 sheet (such as those produced by Avery and other stationery firms) but there's nothing to prevent you from simply printing onto a normal A4 sheet and cutting it up.
These instructions are for Word 2002 but all recent versions should be roughly similar:
Go to Tools > Letters & mailings > Envelopes & Labels.
Select the Labels tab. Click Options.
Change Label Products to 'Avery A4 & A5 Products'
Choose one of the Business Card options from the menu. (The size will be displayed in the right-hand panel).
Click OK.
Choose either 'Full page' or 'Single Label'
Enter your text
To change text size, fonts and colours, highlight the relevant text and select 'Font.
Click Print.
For more professional results try this:
http://www.download.com/DesignPro-Limited-Edit ion/3000-6675_4-10322632.html?tag=lst-0-1
(NB: It's a very big download: Over 50Mb!)
Chris