I guess I've been very lucky over the years when it comes to recording. I never had a problem until switching to Windows XP-Pro, which has so much running in the background that it causes latency problems. I downloaded a free copy of Asio 4-All, which solved the latency problem.
I sincerely believe that most of the recording problems folks encounter have more to do with their lack of knowledge about the computer's operating system, and recording software, than anything else.
Over the years I've used Audacity (free version), Acid Pro 3.0, Acid Pro 4.0 and Mix-Craft 4, all of which do an outstanding job.
One of the secrets to success, however, was to disable everything that is running in computer's background before beginning a recording project. This prevents lots of problems.
Next, purchase a good headphone set, one that fits comfortably and seats firmly around the ears. This prevents any possible of audio looping and feedback.
A high-quality mic for vocals is also a must have item. You cannot expect good vocals from an inexpensive mic. Keep in mind, however, that you DO NOT have to spend a fortune on the mic. There have been several posts on this forum about mics costing under $100 that provide outstanding vocals. The Samson Q7 is among them, and it sells for under $70.
Most of the time, the computer, PC and Mac, have more than adequate sound cards. I've never needed an external sound card to produce excellent recordings--even on the laptops(I own 3).
On the newer laptops, the input circuitry is usually electronically switched between Line and Mic, which usually share the same input jack. Some still have separate Line and Mic jacks, but it's unusual.
Hope this helps,
Gary