Hello friend,
Good news is that XLR mics are generally better than USB mics. however, in order to use one you will need some sort of input into your computer. You can use a USB microphone preamp like the Blue Icicle ($31), a USB mixing board like the Behringer Xenyx 502USB ($60), or a USB tube preamp like the Scarlett ($100). However, each one of these uses a USB output to your computer.
If you CAN'T use a USB at all, then you will have to go through the soundcard on your PC. If you don't have a good sound card then you might want to get one for anywhere from $30 - $50. If that is the case, I suggest getting the Xenyx 502 without USB and the Creative 5.1. Together it will cost you about $85, but will allow you to use the Line in directly to your motherboard.
Now, let's talk mics. You will want an XLR mic. Depending on what option of input you went with, I suggest the:
AT2020 - $99
ATR2500 - $67
MXL 770 - $88
MXL 990 - $96
Samson C01 - $80
Don't forget a Pop filter ($6)
Okay so depending on how you do this here is what you do:
XLR to USB - Plug your XLR mic into the board/preamp and then the USB into your computer.
XLR no USB - Plug the XLR mix into the board/preamp. Use the Line Out of the board/preamp into the Line In on your sound card. You will need a 1/4 to 3.5mm adapter as well to plug into your card.
Hope this helps and let me know if you have any other questions!
::SeaOtterGamer
P.S. - Yes, I know you can get a headset (or mic) that uses a 3.5mm jack and plug it directly into your computer or soundcard. You will get better sound and more capabilities using an XLR setup. Plus, if you use a board like I do, you can adjust your settings on your desk and EQ before recording. It also looks super fancy.