Cheating & Hacking
One way to cheat it to use a hex editor to change some values in your saved game files. Click here to view a brief text file that addresses these possibilities. I myself have never taken the time to manipulate my saved games with a hex editor, so this is all someone else's information. I use the more "graphically appealing" programs, below.
Program Notes/Description
X-COMUTIL by Scott T. Jones
Download (Mirror 1, v9.0)
Download (Mirror 2, v9.0)

The ClarkWehyr editor might be the easiest to use, but Scott Jones' XCOMUTIL lets you change/edit 'everything' in UFO Defense and TFTD. Want to add a new twist to xcom? Different UFOs? Tougher aliens? (or easier) You name it, Scott's done it. XCOMUTIL is always under development, so if there's something you would like to see added, drop Scott a line. Check his page or the first download link for the latest version.

Scott's Webpage

ClarkWehyr Ent. X-COM Editor Suite v1.52
Download (Mirror 1)
(Mirror 2)

Using a nice GUI, this is the simplest saved game editor out there. It allows you to edit many aspects of  X-COM: UFO and X-COM: TFTD saved games, including:  
- Edit money
- Edit, maximize or randomize soldiers' statistics
- Edit base layout and stores
- Edit X-COM craft and stores
- Edit diplomacy/funding data
- Edit base facility data
- Resuscitate dead soldiers
- Import soldiers from X-COM:UFO to X-COM:TFTD
- Intuitive, friendly user interface
- Extensive on-line help
- Mouse support