Hi kutsi,
Actually my main concern is about the HEDL 5540 datasheet. In the datasheet they are showing SN75175 as data receiver. But, when I was reading some of the posts in the forum, I got the feeling that it is somehow possible to connect encoders directly to pic, without any data receiver. I'm new at designing such things and it really confused me...
Yes, the HEDL series encoders has linedrivers in them, thats where the L in the part-number comes from. It's a good idea to use a line reciever chip with them but you dont HAVE to. Just use the two non inverted signal lines (seems to be pin 5 and 7 on my data-sheet) from the encoder and connect them to the PIC - you should be fine with that.

/H.O