Upgrading from 10.4.11 to 10.7. What are the steps and do I also need to pay for 10.5 and 10.6 along the way?

Why do yoy want Lion/10.7???

Anyway, if your Mac meets the requirements you can skip 10.5.x, and even 10.6.x if you can afford to erase all your data.

Snow Leopard/10.6.x Requirements...

General requirements

* Mac computer with an Intel processor

* 1GB of memory (I say 4GB at least)

* 5GB of available disk space (I say 30GB at least)

* DVD drive for installation

* Some features require a compatible Internet service provider; fees may apply.

* Some features require Apple’s MobileMe service; fees and terms apply.

Which apps work with Mac OS X 10.6?...

http://snowleopard.wikidot.com/

It looks like they might still have it...

http://store.apple.com/us/product/MC573Z/A?fnode=MTY1NDAzOA

If it's a core Duo & not a Core2Duo, then it'll only run in 32 bit mode.

Lion/101.7 System requirements

• x86-64 processor (Macs with an Intel Core 2 Duo, Intel Core i3, Intel Core i5, Intel Core i7, or Xeon processor.)

• At least 2GB of memory[14]

• Latest version of Mac OS X Snow Leopard (10.6.8), with the Mac App Store installed

• At least 4GB of disk space for downloading[14]

Like Snow Leopard, Lion does not support PowerPC-based Macs (e.g., Power Macs, PowerBooks, iBooks, iMacs (G3-G5), eMacs).

Lion also does not support 32-bit Intel Core Duo or Core Solo based Macs. Rosetta is no longer available in Lion, which means Lion no longer supports PowerPC applications.

http://en.wikipedia.org/wiki/Mac_OS_X_Lion#System_requirements

http://www.apple.com/macosx/how-to-buy/

What applications are not compatible with Mac OS X 10.7 "Lion"?

http://ow.ly/5Iz09

http://roaringapps.com/apps:table

Yeah, I'd consider a new one, that can hold at least 16 GB of RAM. Sadly, even maxing yours out on 3 GB of RAM & running 10.6.x as the top OS it can run, won't be very satisfactory for use in my experience.

Great news, thanks & good luck! 🙂

I'd also avoid any that have so called integrated graphics, take a gander at iOS 10.8's requirements, you can get an idea where things will be in a couple of more upgrades...

Macs that will support OS X 10.8 Mountain Lion

As usual, the newer the Mac the better:

•MacBook Pro – 13″ from mid 2009 or later, 15″ from late 2007 and newer, 17″ from late 2007 and newer

•MacBook Air – late 2008 and newer

•iMac – models from mid 2007 and newer

•MacBook – 13″ aluminum from 2008, 13″ from 2009 and newer

•Mac Mini – early 2009 and newer

•Mac Pro – early 2008 models and newer

•XServe – early 2009 models and newer

Macs that are NOT expected to support OS X Mountain Lion

Older Macs and those with weaker GPU’s will likely be left behind:

•Anything with an Intel GMA 950 or x3100 integrated graphics card

•Anything with an ATI Radeon X1600

•MacBook models released prior to 2008

•Mac Mini released prior to 2007

•iMac models released prior to 2007

•Original MacBook Air

This list of compatible and incompatible Macs and system requirements are based off of the first OS X Mountain Lion Developer Preview and may be subject to change, we will update when we learn more about the specifics. OS X Mountain Lion will be released this summer but presumably long before that we will know precise system requirements and what Macs are and are not supported by the new version of OS X. Stay tuned.

http://osxdaily.com/2012/02/16/os-x-10-8-mountain-lion-system-requirements/

http://en.wikipedia.org/wiki/OS_X_Mountain_Lion