You have 4 options:
1) connect a dual-port splitter (not dual-line splitter) to the RJ-11 phone cord port. Connect 1 port to the phone as usual, connect the second line to the DVR phone port. Typically requires a really long phone cable.

2) Run a long Ethernet cable from your home router to your DVR's RJ-45 Ethernet Jack.

3) Purchase a wireless router or access point that has Wireless Ethernet Bridge (WET) mode ($40-50). Connect the device to your wireless router, via wireless, and connect the device to your DVR via Ethernet cable to the RJ-45 Ethernet Jack.

See article here:
http://www.dvrplayground.com/article/12254/Converting-a-Linksys-WRT54G-GS-Int...

4) Buy a wireless bridge ($90-100) and do same as option 3.

I used option 3 with a Linksys WRT54GL router w/Thibor 15c firmware, but DD-WRT firmware is easily installed on this router, and better documented and more easily located. You will need the 3rd-party firmware in order to enable bridge mode.