Who knows about sound card? for digitizing music

Hi - Most sound cards I see advertise their output sound quality - but all I care about is input as I am digitizing my LP collection (Linn table connected to phono preamp into sound card). Does it matter for input (i.e. is the motherboard's capability sufficient)? or does it matter, in which case what do people recommend for that? Note I have an (old) Pentium 4 PC so don't have the speed for some of the new cards at high sampling rates. Thanks for any suggestions.
Bypass the sound card and come in via USB with an external DAC box. For about the same investment as a sound card (if that is your goal) you can get a Pro-Ject Phono Box II USB. You will need recording software of some sort like Audacity where you will choose the connected USB Project device as your input. Your bigger problem is not the speed of the P4 processor but that a P4 limits you to XP and older flakey software drivers. Having said that I have done this on XP and it works fine. This Pro-Ject option is a basic solution, not super high end, but it sounds great for what it is. With your Turntable it should sound great. I use a simple program called LP Recorder and bring music in as a wav file. FRom there I divide the tracks with LP Ripper, edit in the track names, and convert to other formats to put in my digital library to have access to a lot of old vinyl on my Sonos or i pod. On my system the result sounds pretty much the same as my original TT playing direct but you have a better TT.