max memory

I am making a C# program... it is intended to run on
Windows XP, Service Pack 2, VS .NET 2003 and .NET framework 1.1, Single Pentium 4 processor, 2 GHz, finally 512MB RAM

I basically want to declare an array (of Int16 and Char if it matters) as big as possible. Now what is a safe assumption as to the maximum amount of memory for the array? and how much time would it take just for declaration and initlization?

maybe an alternative is to delcare some data structure that does not include default values since the array is mostly gonna be 0s (hopefully) anyways. Do i have a choice other than linked-lists?

Why?

Honestly though, i'd like to hear what this would be for....