1) Get yourself a GOOD tape deck. even a fairly old one, you can buy them for really cheap these days; as long as it's got at least Dolby B & C and tape selectors (Normal, Chrome and Metal), it will do the trick. If you can get a Dolby S tape deck or one of the last Pioneer tape decks with digital noise suppressors, you've got the absolute best that money can buy. I remember digitizing audio cassettes using the Creative SBLive! Platinum, connected to a Kenwood Dolby S tape deck, in 1999... man, those were really nice.
I don't know what the frequency response, wow&flutter and dynamic noise ratio is for that "PlusDeck 2c", but I'm willing to bet any serious HiFi home tape deck will spank its ass in terms of sheer audio quality... and there's no limitation concerning the length of the recording (I have 120 minute audio tapes, d'ya think that silly gadget will play them?)
You DON'T want a boombox or a walkman to do the job. Most of these devices have subpar audo quality to begin with, and most of them only have one "headphone" output, which will seriously distort the sound when connected to an external recorder.
2) If you have a GOOD dedicated sound card (Creative SB Live!, Audigy, M-Audio) you don't need any other hardware (and if you're still using on-board sound, you have no excuse, really, *unless* its' an nForce chipset!)
3) Use one "3.5 mm stereo jack to 2 RCA plugs" cable to connect your deck to the soundcard (most likely, this will be the standard equipment configuration)
4) You can use any audio recording software, from freeware (Audacity) to payware (Sony Soundforge)...
In the freeware domain I will probably diverge from the rest of the crowd, and I'll tell you to avoid Audacity. Yes, it's great, but judging from what you ask, you'll probably feel overwhelmed by the complexity of its interface. I've been doing audio editing for a number of years, and I *still* don't like the Audacity interface, I find it much too cluttered. Therefore, I strongly advise you to look at WavePad, dbpoweramp v10 or Audiograbber (the last two offer line-in audio recording capabilities and are also excellent CD rippers and mp3/ogg/FLAC encoders).
As far as payware goes, you can't go wrong with the already mentioned Soundforge, CoolEdit (now rebranded as Adobe Audition) or the lesser-known Goldwave.
If you have a full version of Nero, you might find among its utilities a little program called Nero Wave Editor, which is absolutely fantastic. Similarly, most Creative soundcards I know of come with their own *totally free and more than adequate* software suite for recording and audio editing. I am fairly certain other sound cards makers have similar arrangements.
5) Best of luck, and PLEASE do yourself a favour and experiment a bit, before starting to do the final work, you'll learn a lot in the process, and you'll find that even mistakes can be useful.