You would be correct; I have something in the area of 93,000 observations. 
Thanks for your quick response, I'll continue to try to find a way around this! 
Simon
________________________________________
From: gretl-users-bounces(a)lists.wfu.edu [gretl-users-bounces(a)lists.wfu.edu] on behalf of
Riccardo (Jack) Lucchetti [r.lucchetti(a)univpm.it]
Sent: 16 February 2012 15:27
To: Gretl list
Subject: Re: [Gretl-users] Gretl error/crash
On Thu, 16 Feb 2012, (s) Simon Grenville-Wood wrote:
 Hi,
 I'm currently attempting a multinomial logit model on a large sample of panel data.
 I'm having a problem where I need to be able to create dummies for each
 individual in the sample to control for the individual fixed effects.
 In order to do so while using the logit model, I need to dummify the person ID (PID) in
the sample.
 I've opened the gretl console and I enter the following commands:
 discrete PID      <----transform the variable, 19,421 values, to be discrete
 dummify PID    <----create dummies for each individual to control for fixed effects
 The last command causes gretl to crash, giving a libcairo_32.dll error.
 This happens on whichever computer I am using. Occasionally, if I use
 the menus instead of the console, it will give an 'out of memory' error.
 My PC is definitely sufficiently powerful. 
Is it really? I have no information on how many observations you have in
your dataset, but let's assume for the sake of the argument that you have
80000 (which sounds like a safe bet given that you have nearly 20000
cross-sectional units). You're asking gretl to generate 19421 variables,
each of which will contain 80000 double precision floating-point numbers,
which in turn occupy 8 bytes each. As a result, your newly created
variables would need nearly 11.5 gigabytes of free RAM to be allocated.
This sounds like _a_lot_ of RAM to me.
Riccardo (Jack) Lucchetti
Dipartimento di Economia
Università Politecnica delle Marche
r.lucchetti(a)univpm.it
http://www.econ.univpm.it/lucchetti