Relax. There are free video players on the net. VLC Player, available from VideoLan is one, DivX Player is another, BS Player is a third one although the newer versions install adware which is a compromise many won't make. I recommend the older one--adware free, available on the net if you look around.

Many downloadable videos are DivX because some standalone DVD players (the ones that connect to a TV) can play DivX videos so you can watch them on your computer or your TV.
You should look into purchasing a DivX capable DVD player if you download porn from the net.

[Link]

Features of K-Lite Mega Codec Pack 1.59 :

• Players:
- Media Player Classic [version 6.4.9.0 rev. 611]
• FFDShow:
- ffdshow [rev. 2543]
- extra plugins
- ffdshow VFW interface
• DirectShow video filters:
- XviD [version 1.2.0-dev build 2006-04-20]
- DivX Pro [version 6.2.2]
- CoreAVC [version 0.0.0.4]
- On2 VP6 [version 6.4.2.0]
- On2 VP7 [version 7.0.10.0]
- Cyberlink DVD decoder [version 6.0.0.2023]
- InterVideo DVD decoder [version 7.0.27.191]
- MPEG-1/2 (Ligos) [version 4.0.0.77]
- MPEG-1/2 (Gabest) [version 1.0.0.3]
- MPEG-1/2 (MainConcept) [version 1.0.0.78]
• VFW video codecs:
- XviD [version 1.2.0-dev build 2006-04-20]
- DivX Pro [version 6.2.5.34]
- x264 [rev. 551]
- Windows Media 9 VCM [version 9.0.1.369]
- On2 VP6 [version 6.4.2.0] [Encoding]
- On2 VP7 [version 7.0.10.0] [Encoding]
- Intel Indeo [version 5.2562.15.54]
- Intel Indeo [version 4.51.16.2]
- Intel Indeo [version 3.24.15.03]
- Intel I.263 [version 2.55.1.16]
- huffyuv [version 2.1.1 CCE Patch 0.2.5]
• QuickTime Alternative:
- QuickTime codecs [version 7.0.4.80]
- QuickTime plugin for Internet Explorer
- QuickTime plugin for Firefox/Mozilla/Netscape/Opera
- Extra QuickTime plugins
- QuickTime DirectShow parser
- QuickTime DirectShow decoder wrapper
• Real Alternative:
- RealMedia codecs [version 6.0.12.1483]
- RealMedia plugin for Internet Explorer
- RealMedia plugin for Firefox/Mozilla/Netscape/Opera
- RealMedia DirectShow splitter [version 1.0.1.1]
• DirectShow audio filters:
- MP3 (Fraunhofer) [version 1.9.0.311]
- AC3/DTS/LPCM (AC3Filter) [version 1.08a]
- AC3/DTS/LPCM (InterVideo) [version 7.0.27.191]
- MP1/MP2 (Ligos) [version 4.0.0.77]
- MP1/MP2 (MainConcept) [version 1.0.0.78]
- Vorbis (CoreVorbis) [version 1.1.0.79]
- AAC (CoreAAC) [version 1.2.0.573]
- AAC (3ivX Pro) [version D4 4.5.1]
- MusePack [version 1.0.0.3]
- Monkey's Audio [version 1.00]
- WavPack (CoreWavPack) [version 1.0.3]
- FLAC (illiminable) [version 0.71.0946]
- Voxware MetaSound [version 1.0.0.12]
- AAC encoder (3ivX Pro) [version D4 4.5.1]
• ACM audio codecs:
- MP3 (Fraunhofer) [version 3.3.2]
- MP3 (LAME) [version 3.97b2]
- AC3 (ffcHandler) [version 1.21]
- Vorbis [version 0.0.3.6]
- DivX ;) Audio [version 4.2.0.0]
• DirectShow source filters:
- MP4 splitter (Haali Media Splitter) [1.6.224.23]
- MP4 splitter (Gabest) [version 1.0.0.3]
- Matroska splitter (Haali Media Splitter) [1.6.224.23]
- Matroska splitter (Gabest) [version 1.0.2.9]
- Ogg splitter (Haali Media Splitter) [1.6.224.23]
- FLV splitter (Gabest) [version 1.0.0.1]
- MPEG-TS splitter (Haali Media Splitter) [1.6.224.23]
- MPEG demuxer (Elecard) [version 1.0.31.51211]
- MPEG demuxer (Gabest) [version 1.0.0.3]
- MPEG demuxer (MainConcept) [version 1.0.1.20]
- MPEG demuxer (Ligos) [version 4.0.0.77]
- SHOUTcast Source [version 1.0.0.1]
• DirectShow subtitle filter:
- DirectVobSub (a.k.a. VSFilter) [version 2.37]
- DirectVobSub (a.k.a. VSFilter) [version 2.33]
• DirectShow audio filters (general purpose):
- Matrix Mixer [version 0.30b]
- Morgan Multimedia Stream Switcher [version 0.9.9]
• Encoding tools:
- LAME CLI and DLL [version 3.97b2]
- LameDropXPd [version 3.97b2]
• Tools:
- GSpot Codec Information Appliance [version 2.52 beta 1 build 2004-09-15]
- Sherlock [version 2.0]
- VobSubStrip [version 0.11]
- GraphEdit [build 041201]
- MMCompView [version 1.10]
- AVI Fixed [version 2.0b1]
- FourCC Changer
- Bitrate Calculator

You can download it free, from here

[Link]