Access it for what? If telnet or TiVoWebPlus, forward port 80 (or whatever you have TiVoWeb set to use) and port 21 (for telnet) to the internal IP address of your TiVo.

http://www.portforward.com

For MRV and HMO, don't bother trying. I guess it would be technically possible to get HMO working over the internet, since you can specify an IP address. There is a thread about this somewhere at DealDatabase.

[EDIT]

It is possible to view recordings from outside your network using vserver.

TechLore Blog

HR10-250, Samsung SIR-S4120R, SIR-S4080R, 2 Philips DSR704s (one connected to a Slingbox A/V). One box used the "Zipper"; rest used PTVnet to enable networking features.

Which program would I choose on the port website??

2 DSR7000 Instant Cake, PTV Net, Superpatch For HMO/MRV, Tivo Desktop, and TivoServer.

Another simple and free way to get at your tivo remotely is to use a 3rd party remote access service.  I have tried them all, and found www.logmein.com to perform the best.  To use it you just sign up for an account, download some client software to your home pc, and then login from any remote computer.  It's just like you're sitting at your home pc.  This also works well if your trying to show your wife how to save a file.  

D'Ecosse said:

Yog-Sothoth said: ... [EDIT] It is possible to view recordings from outside your network using vserver.

Technically yes, I guess - But only if you have exceptional upload speed from your home network to your ISP & then reciprocal download speed (likely more easily obtainable) at your remote point. If a 1 hr show is ~ 1MB then that translates to requiring a minimun upload speed of 8,000,000/3600 = 2222Kbps While many ISPs now are 4MB+ in download, the upload is typically only a fraction of this. So the reality is the practicality is not feasible.