Network congestion and moment-to-moment re-routing can cause precisely this kind of inconsistent delivery time. If you're using a public network, there's nothing you can do other than try again later when there may be less traffic. Remember, the Internet was never intended to transmit real-time data such as audio; it's a miracle it works as well as it does.
First, does your sound card play regular Windows sounds? When you start Windows, do you hear the "Ta-Da"? If not, make sure your speakers are plugged in to the "speaker" or "output" jack coming from your sound card. While you're at it, make sure your microphone is plugged into the "mic in" jack. If there is a volume knob on your sound card, make sure it's turned up. If your speakers have a power supply (such as batteries or a power transformer) make sure you have power, such as fresh batteries or the transformer is plugged into a live outlet. Make sure your speakers are turned on. You may need to refer to your sound card or speaker's documentation to get it set up correctly.
Some sound cards come with the microphone input not "turned on". What this means is that your sound card will not "listen" to your microphone until you tell it to. Included with your sound card was (probably) a "Mixer" appliation (if not, there may be a volume control application in your Accessories group.) Double click the Mixer to start it. With Sound Blaster cards, the mixer appears as columns of sliding volume knobs. Your sound card may have come with a different mixer.
If there is a volume control labeled "Microphone", this refers to how much of the sound from the microphone input will come out through your speakers. For now, turn it on (by checking the box or whatever) and set the volume to the same level as the volume control marked "Wave". If you're not sure, just turn it all the way up (you can always turn it down later). Make sure the switch on your microphone is turned on, and tap on it or talk in it. Do you hear yourself? If not, you need to find the input side of the mixer.
Hunt around for a menu option or button called "Recording Controls". When you select it, you'll see a similar looking screen that lists all of the inputs to your system. Turn the microphone input on by clicking the box, and if there is a "gain", set it to its maximum setting. Now, try tapping on the microphone. You should now hear the tapping coming from your speakers. Speak into the microphone, and compare the level of sound from your voice to that of the other sounds in your system.
You want your voice to come out about the same loudness as the "ta-da", and you want it to be intelligible. You may need to adjust the gain downward a bit, or find the correct place to hold your microphone. Some microphones need to be held almost to your lips, while others meant for mounting on your monitor need to be a foot away from your face before you sound good. Experiment with this for a while until the sound coming out of your speakers sounds good to you.
Once you have the microphone gain set, you should return to the output side of your mixer by finding the menu option or button labeled "Volume" or "Output". It might have opened a second window called "Recording Control" or "Input" that you will need to close. Once you get back there, you will probably want to turn the microphone OFF by un-checking the box. This will keep your side of the conversation off of your speaker, preventing nasty feedback squeals. When you've done that, you won't hear anything else from your microphone coming out your speaker, but you now know that your microphone is set up for recording your voice. (Special note to headphone users: if you use headphones, leave the microphone ON. It will help your voice sound better to you, and your conversations will sound more natural. You might wish to adjust the microphone volume setting.)
For a good test, use the "Sound Recorder" program found in your "Accessories" group. You should be able to click on the "Record" dot, say something, click on stop, then rewind, then the play arrow, and hear yourself.
Once your audio hardware is correctly set up and working to your satisfaction, you will probably find that Speak Freely now works surprisingly well. You can use the local loopback facility to verify correct operation with Speak Freely, then proceed to experimenting with an echo server.