I would strongly advise you NOT to use a PA mixer for recording. They are by and large way too noisy. You are better off with a dedicated recording mixer into the sound card if necessary however, this depends entirely on your soundcard and DAW.
For instance, if your sound card has only two analogue inputs and outputs, UNLESS YOU ARE RECORDING A BAND ALL AT ONCE IN STEREO, there is no need for a mixer. You will get infinitely better quality out of a very good stereo preamp. To be sure there are cards with quite good preamps such as the Digidesign or MOTU equipment but this stuff gets a bit pricey and then even with these cards and boxes, a high end pre amp will greatly improve sound quality and detail, tonal character and presence.
If you are recording by yourself and, for the most part, never more than two channels at a time (stereo instruments such as keyboards etc.), then the dedicated pre amp is the way to go. You will hardly be able to get that kind of quality in a mixer with multiple pre amps unless you spend mega bucks. At the very least something on the order of
a Yamaha 01V96 with is over 2k.
If you are recording a band you have a number of choices. You could purchase one of the budget mixers such as a Mackie or Behringer or, it appears Yamaha has a new line of analogue mixers that are quite reasonably priced and if thier reputation is worth anything, might be quite usable gear. Another choice however is something on the order of a MOTU card and box combo. They have combinations that will give you up to 24 analogue ins and outs in a single box and card with room for additional boxes and ins and outs on that card. There is also a software mixer that you can access for the purpose of monitoring.
There is also the Digi 002 or
Digi 002 Rack. I believe there are at least 8 ins ands outs and a number of preamps as well. ALso, you will be using pro tools which, for better or worse, is a srot of de facto standard particularly in certain genres of music.
Lastly, the mixer, whether or not you need to record multiple instruments at a time or not (and by the way, if you only have tow ins and outs, even if you have a mixer, you can record many more instruments but only in stereo so that once you record the instruments, they are set relative to each other and that is that), monitoring is one of the last reasons for a hardware mixer. With the Digi 002, for instance, you will have monitoring. With the MOTU stuff, you will have software monitoring however, contorl will be difficult since you will not have a dedicated volume knob etc.
Another isssue to consider is whether or not you plan to use outboard, hardward effects. If, for instance you want to use an outboard reverb of the non plug-in variety, it will be helpful to have the auxillary sends and returns on a hardware mixer. You can then strap a reverb across a number of channels to hep with the blend of the instrumenst while leaving it off such instruments as bass where it generaly does not belong.
In the end, the entire question is dependant on you finances, goals and recording method. So, use your head and your ears and choose wisely, mistakes are costly in many ways.