Is it possible to have a text box or combo box on an SD card hosted webpage update an internal variable within the loop() section of the program?
ie if I had a variable called isactive how can I get input from a user to change the value to either true or false and have the arduino remember that setting?
If the Arduino is hosting the web page then the response to the HTTP requests will come from your sketch. You can code it to look up whatever values you want for inclusion in the page, and it is up to you whether you store them in voltale memory and look them up from there, or store them persistently in the EEPROM memory.
Changes to that stored value would need to be performed by your sketch too, and it is up to you to decide where the changes are accepted from and implement the mechanism to receive the updates and update the stored configuration. For example, you could receive updated in the form of HTTP requests, or by command over the Arduino's USB serial port.
Thanks for the reply!
Specifically, my intent is to have a webpage accessable over a network that can interact with various people but I need it to have two way interaction.
I have figured out how to get the contents of variables displayed on the webpage dynamically (currently stored information from arduino to webpage) but I can't figure out the easiest way to go the other way (information changes back to the arduino to do something like call a function manually or set the state of a boolean etc).
Lost of examples on how to set the state of a pin remotely, but nothing about internal variables.
I'm new at this and my head is beginning to hurt 
Will the changes come in the form of HTTP requests received by the web server, or are you going to set up some other channel?
I was thinking possibly using an http form to POST the values? Would that work and if so, I know how to create buttons and such but it's the action section that has me fooled here asI have no idea what to put in there. << not an html expert either.
That would work, and you could either code your HTML page to URL encode the variable assignments or put them in the HTTP header. Although you could get it to work using any HTTP request type, it's best practice to use an HTTP Post for transactions that apply a change. You will need to read the incoming URL and/or request header to determine whether the request constitutes an update and which field is being updated.