100Mb Isn't ridiculously huge in terms of ASP.NET usage, but if this is a concern foro you try going to C:\Windows\Microsoft.NEt\Framework\vX.X.X\Config\Machine.config (default location) then look for MemoryLimit="60". You can change this number and it represents % of system Memory that ASP will use.
Also it is important to note that the ASP uses a Garbage collection function that will periodically dispose of unused items thus freeing up memory so its possible that it does not maintain 100MB all the time.
If none of this helps...RAM is cheap, buy more you won't regret it ;)
Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.
Parser Error Message: It is an error to use a section registered as allowDefinition='MachineOnly' beyond machine.config.