I've been having problems with my board ever since I used it as ISP to upload a program to an AVR microchip. I used the Arduino bootloader guide to program the chip. Since then, the software won't upload to my board if I selected 'Arduino UNO' but would upload if I selected 'Arduino Duemilanove w/ Atmega328'. Can anyone explain to me if this is normal after using Arduino as ISP?
This is definitely not normal. The only way I can see this happening is if you accidentally made an Arduino as ISP programmer from the other chip and ended up changing the bootloader on the Uno. Or less likely, that you changed the oscillator on the Uno from the stock 16 MHz one to an 8 MHz one.
My recommendation is to connect an ISP programmer to your Uno and burn the bootloader on it, making sure you have Tools > Board > Arduino/Genuino Uno selected when you do so.