Digital recorders... I use a Sony ICD-P210, which I think is now discontinued. Previously, I had a Sony ICD-P100. The only differences between the two were in recording time (max. 8 hours on the P100, 16 on the P210), and the P210 has a USB interface and software that handles transfers between the recorder and a Windows PC. With the older P100, I would use a patch cable from its earphone/speaker jack into a PC's mic jack and then run a program like Audacity to record the audio as it went into the PC before converting it to MP3. These Sony units record in some other format than WAV, WMA, or MP3 (something called DVF), but the transfer software will convert it to WAV. I then run Audacity with the LAME MP3 plugin to turn those WAVs into MP3s.
If I were going to do this again, I would look for a recorder with a USB interface that functions as a "mass storage device". Some of these recorders will spell that out on the packaging, and this means you do not have to use special software to work with the recorder. It shows up as an external drive on a Windows 2000/XP/Vista system (possibly also Mac OS X, and sometimes Linux), and you can copy or cut the recordings from the recorder and put them on the computer. Some will record directly to the MP3 format, but (IMO) look for at least WAV format. If you can't get something that records in MP3 directly at the price you want, Audacity and the LAME MP3 plugin are free downloads.
As for line inputs... you will most likely not have that as an option except on higher-end recorders. With my Sony recorders, I use a splitter at the radio's speaker jack. I run a short patch cable from one side of the splitter to the recorder, then an earpiece or headphones on the other side of the splitter so I can hear the radio. Then adjust the radio volume so it does not fry your eardrums, and - for my recorders - that is sufficient audio. If you are concerned about the audio level going into a recorder, you can get an "attenuating patch cable" from places like RadioShack to knock the audio level down between the radio and recorder.
Look up my call on QRZ or this site and e-mail me directly if you have further questions. Good luck and 73!
Patrick WD9EWK/VA7EWK http://www.wd9ewk.net/