I see that the repository for the sda4pp plugin went down in 2011. Does anyone know if there is another way to download the plug-in with the repository missing?
If this plug-in is no longer available, does anyone have recommendations for kriging?
Patrick, here is a previous, similar question (for your reference):
SDA4PP 0.201 appears in the older QGIS Contributed Repository in the Plugin Installer for my QGIS (Mac 1.7.4-4). You might want to make sure that repository is being queried and that 'show experimental plugins' is checked.
I think your best bet now is to use the new SEXTANTE plugin, which is a processing framework that can link processes together from different providers (very powerful). You can install it by adding the QGIS New Official Repository's url (http://plugins.qgis.org/plugins/plugins.xml) to Plugin Installer.
You will need to have those packages installed to utilize them inside of SEXTANTE. The manual is in the plugin package's download. Section 7 covers configuring external applications. If you come up with a good script using R for kriging, you might consider submitting it to the plugin author. That section of the manual also covers creating R scripts.