I'm recording my guitar and while I'm playing I can't hear what I'm doing and it makes it tough to get the sound I want. I'm wondering if theres a way to have playback while recording sound?
Procyon's answer is exactly right. Since you have provided no detail about your sound card / interface device, we are only guessing what the answer may be. In other words, what sound card are you using and how are you connecting the guitar to your computer. Also what computer are you using and what operating system? These things are important to giving you the most likely solution to the problem you are having.
Thank you for using the term full duplex (simultaneous input/output). I should have included that my original reply as it means more than what I actually said.
There should be a monitor icon in the mixer view. This might be a speaker or something to that effect. Make sure you are using headphones and make absolute sure you are NOT recording from "what u hear" in the windows mixer, otherwise you could get horrendous feedback that could not only hurt you but seriously damage your hearing. If you aren't using a proper audio interface, it's time to invest. They can be as cheap as $100 or as expensive as several tens of thousands. For $100 you will get a single input or a pair of inputs which are usually a combination mic/line/instrument.
Consider a Line 6 UX1 or even a GX. These have built in amp emulators that sound quite good. These also have proper ASIO(audio stream input output) drivers which will give you much lower latency than your standard sound card. Even better that asio4all.