First you need Aperture 2 or the trial version from Apple. Once you have it, you need to drag the Aperture package and packages folder to the Desktop. Right-click the package and choose Show Package Contents. Open Contents and right-click Aperture (trial).dist; choose Open With and then Other. In the window that displays, choose TextEdit (or your favorite text editor) and scroll all the way to the bottom of the window. Now slowly scroll back up untill you see:
function checkRAMRequirement(RAM)
var requiredRAM = (RAM * 1012 * 1012);
var actualRAM = system.sysctl('hw.memsize');
Change the required RAM to:
function checkRAMRequirement(RAM)
var requiredRAM = (RAM * 256 * 256);
var actualRAM = system.sysctl('hw.memsize');
Save the file and close it. Double-click the Aperture package on the Desktop and follow the instructions to install the program.
After installation, go to your Applications folder and right-click the Aperture application; choose Show Package Contents. Open the Contents folder and then the Resources folder and find minsys.plist; open this file in your favorite text editor. Search for 1000 and replace it with 256. You'll be changing this part of the file:
<key>AELMinimumRAMSize</key>
<dict>
<key>block</key>
<string>1000</string>
</dict>
To this:
<key>AELMinimumRAMSize</key>
<dict>
<key>block</key>
<string>256</string>
</dict>
Save the file then you'll be able to launch Aperture if you have less than 1 GB of RAM.
[kirkmc adds: I haven't tested this. FYI, there's an earlier hint about installing Aperture on unsupported Macs.]

