[R] How to set up multiple spawns of R?

[Guy Perry]

Sorry: resending this; didn't have a title on it.

Trying to set up multiple spawns of R
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Hi.  I'm new to the list but I have a small problem with R.  I'm trying to
set up multiple spawns of R active at the same time on an AMD with a dual
core in Vista so that I can cut down my permutation processing time.  

I've installed R in multiple places, which I thought was the correct way to
do it but whether I use installs at "C:\Program Files\R1" and "C\...\R2", or
even separately on the C: and D: drive, whenever I try to load my package
(qtl), it gives me the error message:

Error in library(qtl) : there is no package called 'qtl'

The thing is, I've installed the packagen in both places (C\...\R1 and
C\...\R2, or both the C: and D: drives) and it still gives me the message. 
Does anyone know how to set up a simultaneous R spawn?  Clearly I'm wrong
about how to get it started.

Thanks,

G Perry