Brad is quite right - you can use them all together. Only thing I want to point out is that NextSTART, DX and LiteStep are very powerful programs with hundreds of different options and abilities, so it might take some time before you fully realize what each program can do. Reading through documentation is always important, more so in some cases than others, granted, but in every case it will enable you to better grasp the potential of each program.
Anyway, I can't speak about the other applications for obvious reasons (I'm sure Jafo will be able to describe LiteStep pretty well, though

) but what I can do is highlight some of the good points in NextSTART, some of them unique to it:
Easy to Install and Run: NextSTART is a desktop enhancement. It does not force you to replace Explorer - it just installs and runs like any other application. NextSTART can, in fact, run on top of any shell, be it Explorer, LiteStep or any other. Simply exit NextSTART for your Windows interface to be automatically returned to normal.
Familiar Default Interface: When run for the first time, NextSTART presents the user with the things the user has always relied on: A Start button, a Task List and the Systray. Everything is still there, but with a completely different (and much better!) look. Open the default NextSTART menu and all the things that were on the Windows Start Menu are there as well (plus some nice extras). As the user grows accustomed to NextSTART, he will be able to change the default interface so that it looks and behaves *exactly* as he wants it to.
Easy to Configure: Every single option in NextSTART can be tweaked via a graphical Preferences panel. No need to learn commands or hand-edit text configuration files. You can also preview changes as you go.
User-Independent Themes: NextSTART themes are totally independent from content. Just download a new NextSTART theme, import it and that's it! Your carefully constructed menus will still be there - but with a completely different theme. No need to re-do anything; it just can't get any easier than this. NextSTART themes are also screen resolution independent.
Hotspots: Hotspots are basically areas on your desktop (or other windows) which are associated to menus, actions or programs. They are a very powerful concept: You can, for instance, have one menu popping up when you click on a specific area of the desktop, another completely different when you bump the left screen edge, yet another when you click on the titlebar of an Excel window, etc... Hotspots can be attached to the desktop, screen edges and even other application windows! Each hotspot can be made to open a menu, run a program or run an Internal NextSTART command. As of NextSTART 2.50, you also have visible hotspot buttons.
Full Drag & Drop support: NextSTART fully supports drag and drop for adding applications, documents and other shortcuts to menus. You can also use drag & drop to re-arrange menu items or copy/move items from one menu to another.
Full Right-click Context Menu support: Just like you do on your Windows Start Menu, you can right click on a NextSTART menu item to perform all sorts of actions on it (Delete, Rename, Scan for Viruses, Show Container, Search, etc...). In fact, basically every option available on Explorer context menus is also available on the NextSTART context menus - all in the gorgeous look provided by your current theme.
Extended Functionality: NextSTART is no toy, nor is it just a pretty face. NextSTART will improve your productivity as well as provide an attractive and functional interface. Unlike with the Windows Start Menu, all your menus are completely configurable. NextSTART allows you to access control panels, applications, system tools, disks, folders, even the entire contents of your desktop or recycle bin with greater ease than before.
Theme Integration: NextSTART integrates very well with other Winstep applications such as WorkShelf. Change a theme in NextSTART and the same theme is automatically applied to WorkShelf (and vice-versa). WorkShelf context menus also use NextSTART skinned menus.
There are, of course, hundreds of other features besides the ones described above. For more information regarding NextSTART, you can read the online User Guide at:
http://www.winstep.net/help/help-ns2/help-ns2.html
Jorge Coelho
NextSTART 2.70 - A user interface that you can actually use!
http://www.winstep.net - Winstep Software Technologies
IRC Chat: #winstep on AustNet